HEMATOLOGY

HEMATOLOGY

A Handbook for Medical Students

BENIGN & MALIGNANT HEMATOLOGY

A connected way of thinking about blood disease

Forewordtop ↑

How the handbook is organised

The handbook is divided into two books. Book One — Benign Hematology covers the foundations (how blood is made and measured), the anemias, the non-malignant white cell disorders, bleeding disorders, thrombosis and anticoagulation, and transfusion medicine. Book Two — Malignant Hematology covers the blood cancers: the founding concepts, the myeloid and lymphoid malignancies, and the cross-cutting treatments of transplantation, supportive care, immunotherapy, and cellular therapy. Chapters are numbered within each book. Every chapter follows the same structure — the big idea, the substance, pitfalls and pearls, a case, and a quick review — so the framework always comes first and the diseases follow as applications of it.

A note on authorship and status

This handbook was created with the assistance of artificial intelligence (Claude, made by Anthropic) as a free study aid for students. It is NOT a peer-reviewed publication, a textbook, or an official clinical reference, and it should not be cited as one. It has not undergone formal editorial or expert review. The content should always be cross-checked against standard textbooks, current clinical guidelines, and your own faculty before being relied upon for examinations or, especially, for patient care. Drug doses and thresholds are deliberately kept general, medicine changes over time, and errors are possible in any AI-assisted material. Where this handbook and an authoritative source disagree, trust the authoritative source.

A High-Yield Guide for Medical Students

How to think about blood before you memorize the diseases

1Blood, Hematopoiesis, and the Lineage Maptop ↑

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Key pathophysiology

Blood has two parts. The formed elements (red cells, white cells, platelets) make up about 45% of volume; plasma, the protein-rich fluid phase carrying clotting factors and immunoglobulins, makes up the rest. Spun in a tube, red cells sink, plasma rises, and a thin grey buffy coat of white cells and platelets sits between them.

Hematopoiesis is the continuous manufacture of these cells—roughly 100 billion new cells per day. It is sustained by HSCs, which have two defining properties: self-renewal (making more stem cells, so the supply never runs out) and multipotency (the ability to generate every blood lineage). HSCs sit quietly in specialized marrow niches; their progeny amplify enormously as they mature.

Commitment is one-directional. The HSC gives rise to a common myeloid progenitor and a common lymphoid progenitor. The myeloid branch produces red cells, platelets (from megakaryocytes), neutrophils, eosinophils, basophils, and monocytes. The lymphoid branch produces B cells, T cells, and natural killer cells. Lineage is steered by growth factors (e.g., erythropoietin for red cells, thrombopoietin for platelets, G-CSF for neutrophils) and master transcription factors.

The lineage map at a glance

Clinical clues

Where blood is made shifts across life: the yolk sac in early embryo, then the fetal liver and spleen, and from the third trimester onward the bone marrow. In adults, active (red) marrow is confined to the axial skeleton—vertebrae, sternum, ribs, pelvis, and proximal femora/humeri. This is why a bone marrow biopsy is taken from the posterior iliac crest, and why marrow stress can cause extramedullary hematopoiesis in the liver and spleen, producing hepatosplenomegaly.

Diagnostic approach

Three tissues support blood and recur throughout the guide. The bone marrow is the factory. The spleen is the quality-control filter that removes aged or abnormal red cells and is a reservoir for platelets—remove it and platelet counts rise and abnormal red cell forms (Howell-Jolly bodies) appear. Lymph nodes and thymus are where lymphocytes mature and mount immune responses, which is why lymphoid malignancies present as lymphadenopathy.

2Red Cell, White Cell, and Platelet Physiologytop ↑

Red cells and hemoglobin

A red cell is essentially a deformable bag of hemoglobin. Its biconcave disc shape maximizes surface area for gas exchange and lets it bend through capillaries narrower than itself. It has no nucleus or mitochondria, so it cannot repair itself and relies on glycolysis for energy—features that matter when we discuss membrane and enzyme disorders later.

Hemoglobin is four globin chains, each cradling a heme group with one iron atom that binds one oxygen molecule. Normal adult hemoglobin is HbA (two alpha, two beta chains). Oxygen binding is cooperative, producing the sigmoid oxygen-dissociation curve: hemoglobin loads oxygen avidly in the lungs and releases it in tissues. The curve shifts right (releasing more oxygen) with acidosis, raised CO2, fever, and raised 2,3-BPG—the body’s way of delivering more oxygen where metabolism is high.

Red cells live about 120 days. Aged cells are removed by splenic macrophages, which recycle iron and break heme down to bilirubin. This is why hemolysis (premature destruction) raises unconjugated bilirubin and LDH while consuming haptoglobin—the lab signature you will use repeatedly.

White cells

Neutrophils dominate and are short-lived (hours in blood), so their numbers swing fast with infection or steroids. Lymphocytes are long-lived and carry immunologic memory. Knowing which cell rises tells you which process is at work: neutrophilia suggests bacterial infection or inflammation, lymphocytosis suggests viral infection, and eosinophilia points to allergy, parasites, or drug reactions.

Platelets and primary hemostasis

Platelets are fragments shed from marrow megakaryocytes under the control of thrombopoietin (made by the liver). They circulate for 7–10 days. When a vessel is injured, platelets adhere to exposed collagen—using von Willebrand factor as molecular glue—then activate, change shape, release granules, and aggregate into a plug. This is primary hemostasis. Defects here (low platelet count or poor platelet function, including von Willebrand disease) cause mucocutaneous bleeding: petechiae, bruising, epistaxis, and heavy periods.

3Reading the Complete Blood Count (CBC)top ↑

The parameters and what they mean

Diagnostic approach: the two-number method for anemia

Step 1 — size (MCV). Microcytic (<80 fL) anemias are dominated by iron deficiency and thalassemia (and, less often, anemia of chronic disease and sideroblastic anemia). Normocytic (80–100 fL) anemias include acute blood loss, hemolysis, anemia of chronic disease, and marrow problems. Macrocytic (>100 fL) anemias split into megaloblastic (B12/folate deficiency) and non-megaloblastic (alcohol, liver disease, hypothyroidism, myelodysplasia, reticulocytosis).

Step 2 — response (reticulocytes). A high reticulocyte count means the marrow is working hard to replace lost cells—pointing to bleeding or hemolysis. A low or inappropriately normal reticulocyte count means the marrow is failing to respond—pointing to a production problem (nutrient deficiency, marrow disease, or lack of erythropoietin). The reticulocyte count is what separates “losing/destroying cells” from “not making enough.”

The RDW adds nuance: it is high when a population of cells varies in size. A high RDW with microcytosis favors iron deficiency (a mix of old normal and new small cells), whereas thalassemia trait classically shows a low/normal RDW with uniformly small cells and a near-normal red cell count.

Clinical clues: common whole-CBC patterns

• Microcytic anemia, high RDW: iron deficiency until proven otherwise—find the bleeding source.
• Pancytopenia (all three lines low): marrow failure, infiltration, megaloblastic anemia, or hypersplenism.
• High WBC with left shift, normal Hb/platelets: reactive neutrophilia (infection, inflammation, steroids).
• High Hb, WBC, and platelets together: suspect a myeloproliferative process
• Isolated thrombocytopenia in a well patient: think ITP, but always confirm it is not a lab artifact (clumping).

4The Blood Filmtop ↑

When to look at the film

Request a film whenever the CBC is unexpectedly abnormal, when hemolysis is suspected, when there is unexplained cytopenia or leukocytosis, or when the analyzer flags abnormal cells. The film is essential—not optional—in any suspected hemolytic anemia, leukemia, or microangiopathy.

A structured way to read red cells

Describe four things in order: size, shape, color, and inclusions. Size gives microcytic, normocytic, or macrocytic; mixed sizes are anisocytosis. Color refers to central pallor—pale (hypochromic) cells suggest low hemoglobin content as in iron deficiency. Shape and inclusions are where the high-yield clues live.

Can’t-miss red cell morphologies

White cells and platelets on the film

Confirm the differential and look for immaturity. A “left shift” (band forms, metamyelocytes) accompanies infection or marrow stress. Blasts or Auer rods mean acute leukemia until proven otherwise. Smudge cells suggest chronic lymphocytic leukemia. For platelets, the film confirms true numbers (clumping causes falsely low counts) and shows large or giant platelets, which suggest rapid turnover or certain inherited disorders.

5Interpreting the Core Hematology Lab Teststop ↑

Iron studies

Four results work together. Ferritin reflects body iron stores—low ferritin is the single most specific test for iron deficiency. Serum iron is the iron in transit. Transferrin (or total iron-binding capacity, TIBC) is the transport protein, which rises in deficiency as the body tries to capture more iron. Transferrin saturation (iron ÷ TIBC) falls in deficiency. The trap: ferritin is an acute-phase reactant and rises with inflammation, infection, and liver disease, so a “normal” ferritin can hide iron deficiency in a sick patient.

The hemolysis panel

To prove hemolysis, look for evidence of red cell breakdown plus a marrow response. Breakdown raises LDH (released from lysed cells) and unconjugated bilirubin (heme catabolism) and consumes haptoglobin (which mops up free hemoglobin, so it falls). The marrow responds with reticulocytosis. Once hemolysis is confirmed, the direct antiglobulin (Coombs) test asks whether it is immune-mediated: positive points to autoimmune hemolysis; negative points to non-immune causes (membrane, enzyme, or mechanical).

• Intravascular hemolysis (destruction within vessels): very low haptoglobin, hemoglobinuria, markedly raised LDH—seen in microangiopathy, transfusion reactions, severe G6PD crises.
• Extravascular hemolysis (destruction in spleen/liver): raised bilirubin, splenomegaly, spherocytes—seen in hereditary spherocytosis and warm autoimmune hemolysis.

Hemoglobin electrophoresis

Electrophoresis and HPLC separate hemoglobins by type and quantify them, confirming hemoglobinopathies and thalassemias. Because this test is so central to red cell disorders, it has its own chapter that follows (Chapter 6). For now it is enough to know it is the confirmatory step after a suggestive CBC and film—microcytosis with normal iron, or sickle cells on the film—and that it must always be read together with the CBC.

The coagulation screen

Two tests map the clotting cascade. The PT (reported as INR) tests the extrinsic and common pathways—factor VII and below; it is prolonged by warfarin, liver disease, and vitamin K deficiency. The aPTT tests the intrinsic and common pathways—factors VIII, IX, XI, XII; it is prolonged by heparin, hemophilia, and von Willebrand disease. When a test is prolonged, the mixing study tells you why: mix patient plasma 1:1 with normal plasma. If it corrects, a factor is deficient (replace the missing factor). If it does not correct, an inhibitor is present (e.g., a factor inhibitor or lupus anticoagulant).

6Hemoglobin Electrophoresistop ↑

Normal hemoglobins and the developmental switch

Hemoglobin is a tetramer: a heme group (iron in protoporphyrin) bound within each of four globin chains. Each red cell carries millions of hemoglobin molecules. Which chains are made changes across life—erythroblasts make a roughly equivalent amount of alpha chains and of the partner chains (beta, delta, gamma), and the partner that dominates shifts with development.

The fetus makes mainly HbF, which then switches to HbA over the first months of life and is nearly complete by about six months. This switch has a key clinical consequence: beta-chain disorders (beta-thalassemia, sickle cell disease) are not apparent at birth because gamma chains are still being made, and only declare themselves after the switch. Alpha-chain disorders, by contrast, affect every hemoglobin (all use alpha chains) and can be detected at birth.

How hemoglobins are separated

Several methods separate hemoglobins, mostly by electrical charge. Traditional gel electrophoresis runs the sample at alkaline (and, to resolve ambiguities, acid) pH. High-performance liquid chromatography (HPLC) is now the standard quantitative method, precisely measuring HbA, HbA2, HbF, and variants. Isoelectric focusing and capillary electrophoresis are also used. The aim in every case is the same: separate the hemoglobin types to diagnose a hemoglobinopathy or thalassemia.

Charge-based methods have a limitation: some variants co-migrate (for example HbS can run with HbD or HbG on an alkaline gel). When a band is ambiguous, confirm it with a second method—an acid gel, HPLC, or a sickle solubility test for HbS.

Quantitative versus qualitative — the core distinction

This is the conceptual heart of the chapter. In thalassemia (quantitative), production of a normal chain is reduced, so the hemoglobin concentration is low and the cells are microcytic, but the mix of hemoglobin types is broadly preserved (with the compensatory shifts described below). In a structural variant such as sickle cell disease (qualitative), the problem is not how much hemoglobin is made but that an abnormal hemoglobin (HbS) is produced—so a new band appears on electrophoresis. Returning to the analogy: thalassemia is too little milk of roughly the normal kind; a variant is a different kind of milk in the carton.

Beta-thalassemia patterns

In beta-thalassemia, beta-chain output is reduced, so unpartnered alpha chains pair instead with delta chains (raising HbA2) and with gamma chains (raising HbF). A raised HbA2 above 3.5% is the hallmark of beta-thalassemia trait. The severity spectrum runs from minor (trait) through intermedia to major. Remember the developmental switch: at birth a beta-thalassemia major patient can have near-normal indices because gamma chains still predominate, and the disease emerges only as HbF falls.

Alpha-thalassemia patterns

Alpha-thalassemia is different because alpha chains are needed for HbA, HbA2, and HbF alike—so reduced alpha output cannot raise A2 or F. The electrophoresis is therefore often normal or shows low-normal HbA2 and HbF, and the diagnosis is frequently one of exclusion (microcytosis with normal iron and a normal or low-A2 pattern), confirmed by genetic testing. When alpha output is severely reduced, excess beta chains pair with each other to form HbH (beta-tetramers), seen in three-gene deletion alpha-thalassemia and accompanied by golf-ball inclusions on a supravital-stained film; in the fetus, excess gamma chains form Hb Barts (gamma-tetramers).

Sickle cell syndromes

Sickle cell disorders are defined by the presence of HbS and by how much normal HbA accompanies it. The single most useful teaching point: in sickle cell trait (HbAS) there is MORE HbA than HbS, whereas in sickle cell disease (HbSS or sickle-beta-0) there is NO HbA at all. Sickle-beta-0-thalassemia behaves like HbSS clinically but adds microcytosis and a raised HbA2/HbF; sickle-beta-plus retains some HbA (but less than 50%) and is usually milder.

Compound heterozygotes and genetic counseling

Inheriting two different abnormal beta genes produces a compound heterozygous state. Sickle-beta-0-thalassemia is the classic example—one sickle gene and one beta-0 gene give no HbA and a phenotype like HbSS. This is why partner testing matters: a mother with sickle trait (HbAS) and a father who is a beta-0-thalassemia carrier can, in a quarter of pregnancies, have a child with sickle-beta-0-thalassemia—clinically significant sickle cell disease. HbSC disease (one sickle, one HbC gene) is another important compound state. Counseling depends on identifying both parents' genotypes.

Interpretation at a glance

7Master Algorithmstop ↑

Algorithm 1 — Approach to anemia

• Confirm anemia and check it is real (not dilutional or a lab error).
• Classify by MCV: microcytic, normocytic, or macrocytic.
• Check the reticulocyte count: high (bleeding/hemolysis) vs low (production problem).
• Direct testing by the box you land in: microcytic → iron studies (± electrophoresis); macrocytic → B12/folate, TSH, liver, film; normocytic with high retics → hemolysis panel ± film; normocytic with low retics → renal function, marrow assessment.
• Always ask “why”: even when you find the type, identify the underlying cause (e.g., the source of blood loss).

Algorithm 2 — Approach to the bleeding patient

• Characterize the bleeding: mucocutaneous (petechiae, bruising, epistaxis, menorrhagia) suggests primary hemostasis; deep bleeds into joints/muscles suggest secondary hemostasis.
• Screen with platelet count, PT, and aPTT; add a film.
• Low platelets → is it production, destruction (e.g., ITP), or sequestration? Confirm it’s not clumping.
• Normal platelets but mucocutaneous bleeding → think von Willebrand disease or a platelet function defect.
• Abnormal PT/aPTT → use the mixing study to separate deficiency from inhibitor; map the pattern to the cascade.

Algorithm 3 — Approach to abnormal counts (high or low)

• For any abnormal line, first ask: reactive (secondary) or clonal (primary)?
• Reactive clues: an obvious trigger (infection, inflammation, iron deficiency, hypoxia, steroids), proportionate changes, and a normal film.
• Clonal clues: very high or persistent counts, multiple lines involved, abnormal/immature cells on the film, splenomegaly, or constitutional symptoms.
• Cytopenias: decide one line versus pancytopenia—pancytopenia raises marrow failure, infiltration, megaloblastic anemia, or hypersplenism.
• When clonal disease is suspected, the bone marrow examination and cytogenetics become the key next step.

Hematologic emergencies — recognize on sight

Looking aheadtop ↑

With these foundations in place—the lineage map, cell physiology, the CBC, the blood film, the core laboratory panels, and the master algorithms—the disease chapters become applications of a framework you already know. Part II turns to the anemias, the largest and most clinically common group, where the two-number method from Chapter 3 does most of the diagnostic work.

A High-Yield Guide for Medical Students

Where the two-number method does most of the work

About Part IItop ↑

Part II applies the framework from Part I to the anemias—the largest and most common group of hematologic problems you will meet. Each chapter keeps the same structure (the big idea, then pathophysiology, clinical clues, diagnosis and management, pitfalls and pearls, a case, and a quick review), and leans on the two-number method—red cell size and reticulocyte response—introduced in Chapter 3. The chapters are numbered continuously from Part I, beginning here at Chapter 8.

8A Structured Approach to Anemiatop ↑

Definition and physiology

Anemia is a reduced hemoglobin concentration—below about 13 g/dL in men and 12 g/dL in non-pregnant women—lowering the blood's oxygen-carrying capacity. Symptoms (fatigue, breathlessness, pallor, palpitations) come from reduced tissue oxygen delivery and from compensation: the heart rate and cardiac output rise, 2,3-BPG increases to unload more oxygen, and erythropoietin drives the marrow. How sick a patient feels depends less on the absolute hemoglobin than on how quickly it fell: a slow drop to 7 g/dL may be well tolerated, while an acute drop to 9 g/dL can cause collapse.

Two ways to classify

The first axis is cell size (MCV); the second is the underlying mechanism—reduced production, increased destruction (hemolysis), or blood loss. The reticulocyte count links the two: it is high when cells are being lost or destroyed and low when production fails.

Diagnostic workup

History targets the cause: blood loss (menstrual, gastrointestinal, including dark stools), diet (vegan, alcohol), drugs, family history (hemoglobinopathy, gallstones, splenectomy), and chronic disease. Examination looks for pallor, jaundice and splenomegaly (hemolysis), koilonychia and glossitis (iron and B12), and lymphadenopathy. Then the labs flow logically: CBC and film, classify by MCV, check reticulocytes, and order targeted tests—iron studies for microcytosis, B12/folate for macrocytosis, a hemolysis panel when reticulocytes are high.

9Iron Deficiency Anemia and Iron Overloadtop ↑

Iron physiology and hepcidin

Dietary iron is absorbed in the duodenum, carried in plasma bound to transferrin, used by erythroid precursors to make hemoglobin, and stored as ferritin. Senescent red cells are broken down by macrophages, which recycle their iron back to plasma—this recycling supplies most daily needs. Hepcidin, made by the liver, is the master regulator: it lowers iron absorption from the gut and blocks release from macrophages by degrading the iron exporter ferroportin. Hepcidin falls in iron deficiency (letting more iron in) and rises in inflammation (trapping iron away), which is the link to anemia of chronic disease.

Causes—and why the cause matters

• Blood loss (most important): menstrual loss in younger women; gastrointestinal loss (ulcer, malignancy) in men and postmenopausal women—this group needs GI evaluation.
• Increased demand: pregnancy, infancy, and rapid growth.
• Malabsorption: celiac disease, gastrectomy, bariatric surgery, H. pylori.
• Inadequate intake: poor diet, contributing rather than acting alone in adults.

Clinical and laboratory features

Beyond general anemia symptoms, iron deficiency produces koilonychia (spoon nails), glossitis, angular cheilitis, pica (craving ice or non-foods), and restless legs. The blood picture is microcytic and hypochromic with a high RDW and often reactive thrombocytosis. Iron studies show low ferritin (the most specific test), low serum iron, high transferrin/TIBC, and low transferrin saturation—remembering that ferritin can be falsely normal or high with coexisting inflammation.

Management

Treat the cause and replace iron. Oral iron is first line; alternate-day dosing improves absorption and tolerability. The expected response is a reticulocyte rise within a week and a hemoglobin rise of about 2 g/dL over three to four weeks—then continue for several months to refill stores. Intravenous iron is used for intolerance, malabsorption, ongoing heavy loss, chronic kidney disease, or when rapid repletion is needed. Failure to respond should prompt rechecking adherence, absorption, and ongoing blood loss.

Iron overload

Too much iron is also harmful. Hereditary hemochromatosis (commonly HFE mutations) causes excess absorption; transfusional overload accumulates in chronically transfused patients (e.g., thalassemia). Excess iron deposits in the liver (cirrhosis), heart (cardiomyopathy, arrhythmia), pancreas and endocrine organs (diabetes, hypogonadism), skin (bronze pigmentation), and joints. Ferritin and transferrin saturation are high. Treatment is therapeutic phlebotomy for hemochromatosis and iron chelation for transfusional overload.

10Anemia of Inflammation (Chronic Disease)top ↑

Pathogenesis

Inflammatory cytokines, especially interleukin-6, drive the liver to make hepcidin. Hepcidin traps iron in macrophages and reduces gut absorption, so serum iron falls even though stores (ferritin) are normal or high. At the same time, cytokines blunt the marrow's response to erythropoietin and modestly shorten red cell lifespan. The result is the anemia seen in chronic infections, autoimmune disease, and malignancy. The most effective treatment is to control the underlying disease.

Telling it apart from iron deficiency

The two can coexist—a high ferritin from inflammation can mask true iron deficiency. A low transferrin saturation with a normal-range ferritin, or a high soluble transferrin receptor, helps unmask combined deficiency.

Anemia of renal failure

Chronic kidney disease causes anemia chiefly through reduced erythropoietin production by the failing kidney (with contributions from uremia and inflammation). It is treated with erythropoiesis-stimulating agents and iron, targeting a modest hemoglobin (around 10–11 g/dL)—not normal levels, because over-correction raises the risk of thrombosis and cardiovascular events.

11Megaloblastic Anemias: B12 and Folatetop ↑

Biochemistry and absorption

Folate and B12 cooperate in DNA synthesis: folate provides one-carbon units for making thymidine, and B12 is required to regenerate the active form of folate (via the methionine synthase reaction). When either is missing, DNA replication stalls while RNA and protein synthesis continue, causing nuclear–cytoplasmic asynchrony—the megaloblastic change. B12 also runs a separate reaction (methylmalonyl-CoA mutase) important for myelin, which is why its deficiency causes neurological disease. Absorption differs: B12 needs intrinsic factor from gastric parietal cells and is taken up in the terminal ileum; folate is absorbed in the jejunum and has small body stores (deficiency develops in months), whereas B12 stores last years.

Causes

Pernicious anemia—autoimmune destruction of parietal cells with anti-intrinsic-factor antibodies—is the classic cause of B12 deficiency and is associated with other autoimmune disease and a long-term gastric cancer risk.

Clinical and laboratory features

Both cause a macrocytic anemia with glossitis, mild jaundice (from ineffective erythropoiesis raising bilirubin and LDH), and, when severe, pancytopenia. B12 deficiency adds neurological features: a peripheral neuropathy, subacute combined degeneration of the cord (dorsal columns—proprioception and vibration loss), and cognitive or psychiatric changes. The blood film shows oval macrocytes and hypersegmented neutrophils (six or more lobes), which can appear before the MCV rises. Confirmatory tests include low B12 or folate, and raised methylmalonic acid (B12-specific) and homocysteine.

Management

Replace the deficient vitamin—B12 by injection (or high-dose oral) and folate orally. The cardinal rule: in combined or unclear deficiency, give B12 before or together with folate, because folate alone can correct the anemia while allowing the neurological damage of B12 deficiency to progress. Watch for hypokalemia as the marrow regenerates and consumes potassium during early treatment.

12Bone Marrow Failure and Aplastic Anemiatop ↑

Approaching pancytopenia

Pancytopenia has two broad mechanisms. Reduced production includes aplastic anemia, myelodysplastic syndromes, marrow infiltration (leukemia, lymphoma, metastatic cancer, fibrosis), and severe megaloblastic anemia. Increased peripheral removal or pooling includes hypersplenism and immune destruction. The reticulocyte count and the bone marrow aspirate and trephine biopsy distinguish an empty marrow (aplastic) from a packed or dysplastic one.

Aplastic anemia

Aplastic anemia is pancytopenia with a hypocellular marrow and no abnormal infiltrate. Most cases are acquired and immune-mediated—cytotoxic T cells attack hematopoietic stem cells. Triggers include drugs (e.g., chloramphenicol, certain anticonvulsants), toxins (benzene), viruses (including seronegative hepatitis), and radiation; many are idiopathic. Inherited marrow failure syndromes (such as Fanconi anemia) present in younger patients and may have congenital anomalies. Clinically, patients show the consequences of each missing line: anemia, infections (neutropenia), and bleeding (thrombocytopenia).

Management

Care has two arms: support and definitive treatment. Support means transfusions (used judiciously), prompt treatment of infection, and removing any offending agent. Definitive treatment depends on age and severity: a young patient with severe disease and a matched sibling donor is offered hematopoietic stem cell transplantation, while others receive immunosuppressive therapy (antithymocyte globulin plus cyclosporine), often with a thrombopoietin agonist. Pure red cell aplasia (an isolated failure of red cell production, linked to parvovirus B19, thymoma, and drugs) is a related but distinct entity.

13Hemolytic Anemias: Overview and Proving Hemolysistop ↑

Proving hemolysis

Look for evidence of red cell breakdown plus a marrow response. Breakdown raises LDH and unconjugated (indirect) bilirubin and consumes haptoglobin, which falls. The marrow responds with a high reticulocyte count, and the film may reveal the mechanism. Together—high reticulocytes, high LDH, high indirect bilirubin, low haptoglobin—these confirm hemolysis before you ask why.

Localizing: intravascular versus extravascular

A classification you can reproduce

Inherited hemolysis reflects an intrinsic red cell defect: the membrane (hereditary spherocytosis), an enzyme (G6PD, pyruvate kinase), or the hemoglobin (sickle cell, thalassemia). Acquired hemolysis is usually an extrinsic assault: immune (autoimmune, alloimmune, drug-induced), mechanical (microangiopathy, prosthetic valves), infection (malaria), or the acquired membrane defect of paroxysmal nocturnal hemoglobinuria. After proving hemolysis, the direct antiglobulin test sorts immune (positive) from non-immune (negative) causes and directs the rest of the workup.

14Hereditary Hemolytic Anemias: Membrane and Enzyme Defectstop ↑

Hereditary spherocytosis

A defect in membrane-skeleton proteins (commonly spectrin or ankyrin) makes the red cell lose surface area, rounding into a spherocyte. Spherocytes are stiff and are trapped and destroyed in the spleen (extravascular hemolysis). Patients have anemia, jaundice, splenomegaly, and pigment gallstones; severity ranges from mild to transfusion-dependent. The film shows spherocytes, the MCHC is characteristically high, and the direct antiglobulin test is negative (distinguishing it from autoimmune hemolysis). Diagnosis is supported by the EMA-binding test or osmotic fragility. Management is folate supplementation, with splenectomy reserved for more severe disease (after vaccination, given the infection risk).

G6PD deficiency

Glucose-6-phosphate dehydrogenase protects red cells from oxidative stress by generating NADPH. The deficiency is X-linked (affecting mainly but not only males) and common in once malaria-endemic regions. Most of the time patients are well, but exposure to an oxidant—certain drugs (primaquine, dapsone, sulfonamides, nitrofurantoin), fava beans, or infection—triggers acute, often intravascular, hemolysis. The film during a crisis shows bite cells and blister cells, and Heinz bodies (denatured hemoglobin) on supravital staining. Management is to identify and remove the trigger and provide supportive care; enzyme levels should be measured after recovery, since they can be falsely normal during an acute episode when the most deficient cells have already lysed.

Pyruvate kinase deficiency

The most common glycolytic enzyme defect, pyruvate kinase deficiency is autosomal recessive and reduces ATP production, causing a chronic non-spherocytic hemolytic anemia of variable severity, with extravascular hemolysis and splenomegaly.

15The Thalassemiastop ↑

Genetics and pathophysiology

Hemoglobin needs balanced production of alpha and beta chains. In beta-thalassemia (usually point mutations) beta-chain output is reduced, so excess alpha chains precipitate and damage red cell precursors. In alpha-thalassemia (usually gene deletions—there are four alpha genes) alpha output is reduced, and excess beta or gamma chains form unstable tetramers (HbH or Hb Barts). The shared theme is chain imbalance causing ineffective erythropoiesis and hemolysis.

Beta-thalassemia

• Beta-thalassemia minor (trait): one affected gene; mild or no anemia, marked microcytosis with a high red cell count, and raised HbA2—important mainly for genetic counseling.
• Beta-thalassemia intermedia: moderate anemia, not regularly transfusion-dependent.
• Beta-thalassemia major (Cooley anemia): severe transfusion-dependent anemia from infancy, with marrow expansion (frontal bossing, “hair-on-end” skull), extramedullary hematopoiesis, hepatosplenomegaly, and—from transfusions and increased gut absorption—iron overload.

Alpha-thalassemia

Severity depends on how many of the four alpha genes are lost: one (silent carrier), two (alpha-thalassemia trait, microcytosis), three (HbH disease, a moderate-to-severe hemolytic anemia with beta-tetramers and golf-ball inclusions), and four (Hb Barts, causing hydrops fetalis and death in utero unless treated).

Diagnosis and management

The indices are a strong clue: a low MCV with a high-normal or high red cell count and only mild anemia (a low Mentzer index) suggests thalassemia over iron deficiency. Confirm with hemoglobin electrophoresis/HPLC (raised HbA2 in beta-trait) and, where needed, genetic testing. Management ranges from none (trait, plus counseling) to regular transfusion with iron chelation in major disease, folate supplementation, judicious splenectomy, and curative hematopoietic stem cell transplantation in selected children. A practical pitfall: never mistake thalassemia trait for iron deficiency and treat with long-term iron.

16Sickle Cell Diseasetop ↑

Genetics and pathophysiology

Sickle cell disease arises from a single point mutation in the beta-globin gene (glutamate to valine at position 6). Homozygotes (HbSS) have the most severe disease; heterozygotes (HbAS, sickle trait) are generally asymptomatic carriers; compound heterozygotes include HbSC disease and sickle-beta-thalassemia. When oxygen is low, HbS molecules polymerize into rigid fibers that distort the cell; repeated sickling stiffens membranes, promotes adhesion to the endothelium, and triggers vaso-occlusion and inflammation, while the damaged cells undergo hemolysis. Dehydration, acidosis, infection, cold, and hypoxia precipitate sickling.

Acute complications

• Vaso-occlusive (pain) crisis: the hallmark—severe bone and tissue pain from microvascular occlusion.
• Acute chest syndrome: fever, chest pain, hypoxia, and a new pulmonary infiltrate—a leading cause of death; treat aggressively.
• Stroke: especially in children; transcranial Doppler screening identifies risk.
• Splenic sequestration: sudden splenic pooling of blood with a falling hemoglobin—life-threatening in young children.
• Aplastic crisis: parvovirus B19 shuts down red cell production atop chronic hemolysis.
• Infection: functional asplenia raises risk from encapsulated organisms (pneumococcus); a major cause of childhood death.
• Priapism: a urological emergency.

Chronic organ damage

Years of vaso-occlusion and hemolysis damage many organs: the kidney (impaired concentrating ability, papillary necrosis), the retina (proliferative retinopathy), bones (avascular necrosis of the femoral head), the lungs (pulmonary hypertension), and skin (leg ulcers). The spleen progressively infarcts, producing autosplenectomy and Howell-Jolly bodies on the film.

Diagnosis and management

Diagnosis is by newborn screening and hemoglobin electrophoresis/HPLC (HbS predominant with little or no HbA in disease; see Chapter 6), supported by sickle solubility testing. Management combines prevention and treatment: hydroxyurea raises protective HbF and reduces crises and acute chest syndrome; transfusion (simple or exchange) treats and prevents severe complications such as stroke; penicillin prophylaxis and vaccination guard against infection; and acute crises need analgesia, hydration, oxygen, and treatment of triggers. Folate is given for chronic hemolysis. Newer agents (voxelotor, crizanlizumab, L-glutamine) add options, and hematopoietic stem cell transplantation or gene therapy can be curative in selected patients.

17Acquired Hemolytic Anemias: Autoimmune and Microangiopathictop ↑

Autoimmune hemolytic anemia (AIHA)

Antibodies against red cell antigens drive destruction, and the temperature at which they bind defines the two types.

Warm AIHA is the more common form: IgG-coated cells are removed in the spleen, the film shows spherocytes, and the direct antiglobulin test is positive for IgG. First-line treatment is corticosteroids, with rituximab and splenectomy as later options. Cold agglutinin disease is mediated by IgM that fixes complement in cooler peripheries, causing agglutination and often intravascular hemolysis; steroids work poorly, so management centers on keeping the patient warm, treating any underlying infection or lymphoma, and using rituximab.

Microangiopathic hemolytic anemia (MAHA)

When red cells are forced through vessels partly occluded by microthrombi or damaged endothelium, they fragment into schistocytes. MAHA with thrombocytopenia defines the thrombotic microangiopathies—thrombotic thrombocytopenic purpura (TTP), hemolytic uremic syndrome (HUS), and disseminated intravascular coagulation (DIC)—covered in the thrombosis section. TTP (from severe ADAMTS13 deficiency) is a particular emergency: schistocytes plus thrombocytopenia should trigger urgent plasma exchange, not platelet transfusion. Mechanical heart valves can cause a similar fragmentation hemolysis.

Other acquired causes

Paroxysmal nocturnal hemoglobinuria is an acquired stem cell mutation (PIGA) that strips complement-protective proteins from blood cells, causing intravascular hemolysis, thrombosis, and cytopenias; it is diagnosed by flow cytometry. Infections (notably malaria) and certain drugs are further acquired causes.

Looking aheadtop ↑

The anemias covered here account for the great majority of red cell disease you will encounter. Part III turns to the non-malignant white cell disorders—neutropenia, neutrophil dysfunction, and the reactive leukocytoses and eosinophilia—where the central question shifts from red cell size to whether a count change is reactive or clonal.

One question above all: reactive or clonal?

About Part IIItop ↑

Part III covers the non-malignant disorders of white cells—chiefly the neutrophils. Two themes run through it. First, too few functioning neutrophils (whether from low numbers or poor function) means infection risk, and the absolute neutrophil count is the number that matters. Second, when white cell counts are high, the single most useful question is whether the rise is reactive (a normal, polyclonal response to something) or clonal (a primary blood malignancy). The malignant white cell disorders themselves—leukemias, lymphomas, myeloma, and the myeloproliferative and myelodysplastic neoplasms—belong to the companion malignant hematology guide.

18Neutropenia and Neutrophil Function Disorderstop ↑

The neutrophil and the ANC

Neutrophils mature in the marrow over about a week, then circulate only briefly (hours) before entering tissues. In the blood they exist in two pools—circulating and marginated (stuck to vessel walls)—which is why stress, exercise, or adrenaline can transiently raise the count by demargination. What counts clinically is the absolute neutrophil count: the total WBC multiplied by the percentage of neutrophils (and bands).

Note benign ethnic neutropenia (associated with the Duffy-null genotype) is very common in Middle East: a mild, lifelong neutropenia with no increased infection risk that should not be over-investigated or mistaken for disease.

Causes of neutropenia

• Decreased production: marrow failure or infiltration, chemotherapy and many drugs, B12/folate deficiency, and congenital syndromes (severe congenital neutropenia, cyclic neutropenia).
• Increased destruction or margination: immune/autoimmune neutropenia, Felty syndrome, and many infections (especially viral and overwhelming sepsis).
• Sequestration: hypersplenism.

Drugs are the single most important acquired cause—chemotherapy predictably, but also idiosyncratic reactions to antithyroid drugs, sulfonamides, antipsychotics (clozapine), and others. A careful medication history is essential.

Clinical features and risk

Neutropenic patients lose the ability to mount pus and localize infection, so signs can be subtle. Mouth ulcers, gingivitis, and perianal infection are common, and bacteremia can progress rapidly. Febrile neutropenia—fever with an ANC below 0.5 ×10⁹/L—is a medical emergency requiring immediate broad-spectrum antibiotics before results return, because untreated sepsis in this setting can be fatal within hours.

Approach and management

Assess with a drug and infection history, examination of mucosa and skin, the trend and chronicity of the count, and a blood film; a bone marrow examination is reserved for unexplained or severe cases. Management is cause-directed: stop the offending drug, treat infection promptly, and use granulocyte colony-stimulating factor (G-CSF) to shorten severe neutropenia or in congenital disease. The cornerstone remains rapid empirical antibiotics for febrile neutropenia.

Qualitative (functional) neutrophil disorders

Here the count is normal but the cells do not work, producing recurrent infections despite adequate numbers. Chronic granulomatous disease results from a defective NADPH oxidase, so neutrophils cannot generate the oxidative burst—patients suffer infections with catalase-positive organisms (Staphylococcus aureus, Aspergillus) and form granulomas; the dihydrorhodamine (or older nitroblue tetrazolium) test is diagnostic. Leukocyte adhesion deficiency prevents neutrophils from leaving the bloodstream, causing delayed umbilical-cord separation, infections without pus, and a high blood neutrophil count. Chediak-Higashi syndrome shows giant granules, partial albinism, and recurrent infection.

19Reactive Leukocytosis and Eosinophiliatop ↑

Definitions and the central question

Leukocytosis is an increased total white cell count; more useful is to name which lineage is raised, because each has its own differential. Reactive (secondary) leukocytosis is a polyclonal response to a stimulus; clonal (primary) leukocytosis comes from a malignant clone.

Neutrophilia, lymphocytosis, monocytosis

Neutrophilia is most often reactive—infection, inflammation, corticosteroids, smoking, and physical stress; a left shift and toxic granulation support a reactive cause. Persistent, unexplained neutrophilia warrants screening for a clonal process. Lymphocytosis in children and young adults is usually viral (classically EBV with atypical lymphocytes); in older adults a persistent mature lymphocytosis suggests chronic lymphocytic leukemia, identified by smudge cells and confirmed by flow cytometry. Monocytosis accompanies chronic infections, autoimmune disease, and marrow recovery, but a persistent unexplained rise can signal chronic myelomonocytic leukemia.

Eosinophilia

Eosinophilia is graded mild (0.5–1.5), moderate, and severe; hypereosinophilia is a count above 1.5 ×10⁹/L on repeated testing or in tissue. The causes are best remembered by category: allergy and atopy (asthma, eczema), drug reactions, parasitic and some other infections, connective tissue disease and vasculitis (e.g., eosinophilic granulomatosis with polyangiitis), malignancy (reactive to lymphoma/solid tumors, or clonal in myeloid neoplasms), and adrenal insufficiency. In broad terms, eosinophilia is secondary (reactive, the commonest), primary (clonal, part of a myeloid neoplasm), or idiopathic (hypereosinophilic syndrome).

What makes eosinophilia dangerous is end-organ damage: persistently high eosinophils infiltrate and injure the heart (endomyocardial fibrosis), lungs, skin, and nerves, independent of the cause. The workup confirms persistence, excludes secondary causes (history, parasites, drugs), and then evaluates for a clonal myeloid disorder. Treatment targets the cause; corticosteroids are used for symptomatic or organ-threatening disease—but exclude (or empirically treat) Strongyloides first, because steroids can precipitate fatal hyperinfection.

Read the bleeding pattern, then the cascade

About Part IVtop ↑

Part IV turns from cells to clotting. Hemostasis is a staged system—platelets and vessels stop bleeding quickly (primary hemostasis), the coagulation cascade lays down a stable fibrin clot (secondary hemostasis), and fibrinolysis later clears it. Every bleeding disorder is a defect in one of these stages, and the pattern of bleeding usually tells you which. These chapters build that framework and then work through the disorders of platelets and clotting factors. Thrombosis and anticoagulation follow in Part V.

20Principles of Hemostasistop ↑

Primary hemostasis

When a vessel is injured it first constricts. Platelets then adhere to exposed subendothelial collagen, using von Willebrand factor (VWF) as the molecular bridge between collagen and the platelet GpIb receptor. Adhesion activates the platelets: they change shape, release the contents of their granules (recruiting more platelets), and link to one another through GpIIb/IIIa receptors that bind fibrinogen. The result is a platelet plug. Defects at this stage—low platelet numbers, poor platelet function, or VWF deficiency—cause mucocutaneous bleeding.

Secondary hemostasis

In parallel, the coagulation cascade generates thrombin, which converts fibrinogen into fibrin to stabilize the plug. Traditionally the cascade is drawn as two arms feeding a common pathway, and this still maps neatly onto the screening tests: the intrinsic pathway (factors XII, XI, IX, VIII) is measured by the aPTT, the extrinsic pathway (factor VII with tissue factor) by the PT, and both converge on the common pathway (factors X, V, II/prothrombin, and fibrinogen). Physiologically, coagulation is better understood as a cell-based process: tissue factor initiates a small amount of thrombin, which amplifies the response on the activated platelet surface and drives a thrombin burst that produces a robust fibrin clot. Factors II, VII, IX, and X (and the regulators protein C and S) depend on vitamin K.

Regulation and fibrinolysis

Clotting is kept in check by natural anticoagulants—antithrombin, the protein C/protein S system, and tissue factor pathway inhibitor—which confine the clot to the site of injury (their deficiency causes thrombosis, covered in Part V). Later, plasmin breaks fibrin down into fragments, including D-dimer, restoring normal flow. Bleeding can therefore result not only from too little clotting but occasionally from excessive fibrinolysis.

Clinical correlation

21Approach to the Bleeding Patienttop ↑

History: what to ask

Ask where bleeding occurs (skin and mucosa versus joints and muscles), how long it has been a problem (since childhood suggests an inherited disorder; recent onset suggests an acquired one), and how the patient handled hemostatic challenges—dental extractions, surgery, childbirth, circumcision, and menstruation. A lifelong history of bleeding only with major challenges differs from spontaneous bleeding. Family history points to inherited disorders and their inheritance pattern, and a drug history is essential: antiplatelet agents, anticoagulants, and many over-the-counter drugs cause or unmask bleeding. Structured bleeding-assessment scores help quantify whether the history is truly abnormal.

Recognizing the pattern

Testing strategy

Start with the screen: a platelet count, PT, aPTT, and fibrinogen, alongside a blood film. Interpret these with the master algorithm from Chapter 6—if a clotting time is prolonged, a mixing study separates factor deficiency (corrects) from an inhibitor (does not). Then move to specific tests: von Willebrand studies, individual factor assays, and platelet function testing. A crucial point: a normal screen does not exclude a bleeding disorder. Von Willebrand disease, mild factor deficiencies, platelet function defects, and factor XIII deficiency can all bleed with a completely normal platelet count, PT, and aPTT—so a convincing history justifies specialized testing even when the screen is normal.

22Thrombocytopenia and Immune Thrombocytopenia (ITP)top ↑

A framework for low platelets

Two artifacts and three emergencies must be addressed up front. The artifact is pseudothrombocytopenia from EDTA-induced platelet clumping—always confirm a low count on the film. The emergencies are thrombotic thrombocytopenic purpura (schistocytes), disseminated intravascular coagulation (abnormal clotting times, low fibrinogen), and heparin-induced thrombocytopenia (recent heparin, thrombosis)—all covered in Part V and all needing specific, urgent action.

Immune thrombocytopenia (ITP)

ITP is caused by autoantibodies that both accelerate platelet destruction and impair their production. It may be primary or secondary to another condition (HIV, hepatitis C, lupus, chronic lymphocytic leukemia, certain drugs, and H. pylori). The presentation differs by age: in children it is often acute and post-viral and resolves spontaneously, whereas in adults it tends to be chronic. The hallmark is isolated thrombocytopenia—a low platelet count with otherwise normal blood lines and film—in a patient who is clinically well apart from mucocutaneous bleeding. There is no confirmatory test; ITP remains a diagnosis of exclusion.

Management

Treat the patient, not just the number—many patients with moderate thrombocytopenia and no bleeding can be observed. Treatment is indicated for significant bleeding or very low counts. First-line therapy is corticosteroids, with intravenous immunoglobulin (IVIG) added when a faster rise is needed (for example before a procedure or with active bleeding). Second-line options include thrombopoietin-receptor agonists, rituximab, and splenectomy. Life-threatening bleeding is treated with combined platelet transfusion, IVIG, and corticosteroids.

23Qualitative Platelet Disorderstop ↑

How platelets can fail

Recall the steps of platelet function: adhesion to the vessel wall (via GpIb and VWF), activation and shape change, secretion of granule contents, and aggregation (via GpIIb/IIIa and fibrinogen). A defect at any step impairs the platelet plug. Because the platelet count and the coagulation screen are normal, these disorders are diagnosed by specialized platelet function testing.

Acquired platelet dysfunction (common)

Drugs are the leading cause. Aspirin irreversibly inhibits cyclooxygenase, blunting platelet aggregation for the life of the platelet; P2Y12 inhibitors (clopidogrel) and other antiplatelet agents act on different steps, and NSAIDs cause reversible inhibition. Systemic conditions also impair platelets: uremia (kidney failure), liver disease, cardiopulmonary bypass, and myeloproliferative neoplasms. A careful drug and comorbidity history usually identifies the cause.

Inherited platelet disorders (rare but instructive)

Diagnosis and management

Diagnosis rests on platelet function testing—light transmission aggregometry is the reference method, showing characteristic patterns (for example, absent aggregation to all agonists in Glanzmann thrombasthenia). The coagulation screen is normal. Management starts with removing the offending drug and treating any underlying condition; bleeding is reduced with desmopressin (which improves platelet function in some disorders), antifibrinolytic agents (tranexamic acid), and—for severe bleeding or surgery—platelet transfusion.

24Von Willebrand Diseasetop ↑

VWF biology

VWF is made by endothelial cells and megakaryocytes and circulates as large multimers—the bigger the multimer, the more effective. It performs primary hemostasis by bridging the platelet GpIb receptor to subendothelial collagen, and it acts as a chaperone for factor VIII, prolonging its half-life. This dual role explains the laboratory picture: severe VWF deficiency lowers factor VIII enough to prolong the aPTT, even though the primary problem is in primary hemostasis.

Types

Two subtypes are worth remembering. Type 2B has a gain-of-function VWF that binds platelets in the circulation, causing thrombocytopenia. Type 2N has VWF that cannot bind factor VIII, so factor VIII is low and the picture mimics hemophilia A (but with autosomal, not X-linked, inheritance).

Clinical features

Inheritance is usually autosomal, so unlike hemophilia it affects both sexes. Bleeding is mucocutaneous: epistaxis, easy bruising, heavy menstrual bleeding, and bleeding after dental work or surgery. Severity varies widely, and mild disease may only show up under hemostatic challenge.

Diagnosis and management

Testing measures VWF antigen (how much VWF), VWF activity (how well it works—ristocetin cofactor or GpIb-binding assays), and factor VIII; multimer analysis defines the subtype. The platelet count is usually normal (except type 2B), and the aPTT may be normal or prolonged depending on the factor VIII level. Management depends on type and severity: desmopressin releases stored VWF and is effective in many type 1 patients (test responsiveness first; avoid in type 2B, where it can worsen thrombocytopenia), while VWF-containing concentrates are used for severe disease, type 3, and surgery. Antifibrinolytics help with mucosal bleeding, and pregnancy and procedures need specific planning.

25Hemophilia, Factor Deficiencies, and Rare Bleeding Disorderstop ↑

Hemophilia A and B

Both are inherited in an X-linked recessive pattern, so they predominantly affect males, with females usually carriers (who can nonetheless bleed if factor levels are low). Hemophilia A (factor VIII) is far more common than hemophilia B (factor IX); clinically the two are indistinguishable. Severity tracks the residual factor level.

The hallmark is deep bleeding: recurrent hemarthrosis (often into the same target joints, leading to chronic arthropathy), muscle hematomas, and, dangerously, intracranial and retroperitoneal bleeds; surgical and dental bleeding is delayed and prolonged. The laboratory shows a prolonged aPTT with a normal PT, platelet count, and VWF; the aPTT corrects on a mixing study (a deficiency, not an inhibitor), and a specific factor assay distinguishes A from B.

Management

Treatment replaces the missing factor, either on demand for bleeds or as regular prophylaxis to prevent hemarthrosis in severe disease. For hemophilia A, the non-factor agent emicizumab (a bispecific antibody that mimics factor VIII) has transformed prophylaxis, and desmopressin can raise factor VIII enough to cover minor procedures in mild disease. Antifibrinolytics are useful adjuncts for mucosal and dental bleeding, and gene therapy is emerging. The feared complication is the development of inhibitors—alloantibodies against the infused factor that render replacement ineffective and require bypassing agents and immune tolerance strategies.

Acquired hemophilia

Acquired hemophilia is a separate entity: autoantibodies against factor VIII arise in a previously normal person—often an older adult or postpartum woman—causing sudden, severe bleeding. The aPTT is prolonged and, crucially, does NOT correct on mixing (an inhibitor). Treatment combines control of bleeding with bypassing agents and immunosuppression to remove the antibody.

Other factor deficiencies and rare disorders

Factor XI deficiency (common in Ashkenazi Jews) causes variable, often trauma-related bleeding. Factor XIII deficiency is unique: it stabilizes the clot, so the PT and aPTT are normal but patients have delayed bleeding, classically umbilical-stump bleeding in neonates and a risk of intracranial hemorrhage. Fibrinogen disorders, factor VII deficiency, and combined deficiencies also occur. Acquired multifactor problems are far more common in practice: vitamin K deficiency (factors II, VII, IX, X) and liver disease (most factors), both prolonging the PT. Tranexamic acid is a valuable adjunct across many of these bleeding disorders.

When clotting happens in the wrong place

About Part Vtop ↑

Part IV asked why patients bleed; Part V asks the opposite—why they clot when they should not, and how we safely prevent and treat that. The same hemostatic system, pushed the other way, produces venous and arterial thrombosis. These chapters cover the approach to thrombosis and inherited thrombophilia, the anticoagulant and antiplatelet drugs you will prescribe and reverse, and two disorders where low platelets paradoxically signal clotting: heparin-induced thrombocytopenia and the thrombotic microangiopathies

26Approach to Thrombosis and Thrombophiliatop ↑

Virchow's triad and the spectrum of thrombosis

Venous thromboembolism (VTE) spans deep vein thrombosis (DVT) and pulmonary embolism (PE)—the same disease at two sites. Venous clots are fibrin-rich red clots that form in slow-flowing blood and are treated with anticoagulants; arterial clots are platelet-rich white clots that form on ruptured plaques and are treated with antiplatelet agents. Knowing which kind of clot you are facing guides the whole approach.

Risk factors: provoked versus unprovoked

The first question in any VTE is whether it was provoked. Provoking factors include recent surgery, immobility or hospitalization, active cancer, pregnancy and the postpartum period, estrogen therapy, trauma, and long-haul travel. A clot with a clear, reversible provoker behaves differently—and is treated for a shorter time—than an unprovoked clot, which carries a higher recurrence risk. Active cancer deserves special mention as both a strong provoker and a reason for extended anticoagulation.

Inherited and acquired thrombophilia

When to test—and the traps

Resist reflexive thrombophilia screening. For most provoked clots, the result does not change management—the duration of anticoagulation is decided by whether the clot was provoked and by bleeding risk, not by an inherited mutation. Testing also has timing pitfalls: an acute clot and anticoagulant drugs distort many assays (protein C/S and antithrombin levels fall acutely; heparin and warfarin interfere), so tests done at the wrong moment mislead. The important exception is antiphospholipid syndrome, which is acquired, causes both arterial and venous thrombosis and pregnancy loss, and does change management (often indefinite anticoagulation, with warfarin preferred over DOACs).

Diagnosis of VTE

Combine clinical probability with testing. A validated score (such as the Wells score) sets the pretest probability. A D-dimer is sensitive but not specific—useful to rule out VTE when probability is low (a normal D-dimer excludes it) but unhelpful when probability is high. Imaging confirms: compression ultrasound for DVT and CT pulmonary angiography for PE.

27Anticoagulant and Antiplatelet Therapytop ↑

Antiplatelet agents

Aspirin irreversibly inhibits cyclooxygenase, reducing platelet aggregation for the platelet's lifespan. P2Y12 inhibitors (clopidogrel, ticagrelor, prasugrel) block ADP-mediated activation, and glycoprotein IIb/IIIa inhibitors are potent intravenous agents used in selected acute settings. These drugs are the mainstay for arterial disease—acute coronary syndromes, ischemic stroke, and coronary stents (often as dual antiplatelet therapy).

Anticoagulants

A few practical points anchor these drugs. Heparins act immediately and are used to initiate treatment; low-molecular-weight heparin has predictable pharmacokinetics and rarely needs monitoring. Warfarin is cheap and reversible but has a narrow therapeutic window, countless food and drug interactions, and a delayed onset—so it requires overlapping (bridging) cover when started for acute clot. Direct oral anticoagulants (DOACs) are now first-line for most VTE and atrial fibrillation: fixed dosing, no routine monitoring, and specific reversal agents.

Choosing therapy and special populations

Treatment duration for VTE depends on the provoker: a provoked clot is typically treated for about three months, while an unprovoked clot or cancer-associated thrombosis often warrants extended therapy. Special situations matter: in pregnancy, low-molecular-weight heparin is used because warfarin is teratogenic and DOACs are avoided; in significant renal impairment, dosing must be adjusted (DOACs and LMWH are renally cleared); and antiphospholipid syndrome favors warfarin over DOACs. The universal complication is bleeding, which is why knowing each agent's reversal is essential.

28Heparin-Induced Thrombocytopenia (HIT)top ↑

Pathophysiology

Heparin can bind platelet factor 4 (PF4) to form a complex that the immune system attacks. The resulting IgG antibodies bind the PF4-heparin complex and cross-link platelet receptors, activating platelets en masse. This both consumes platelets (the thrombocytopenia) and generates a powerfully prothrombotic state (the thrombosis). It is counterintuitive precisely because the falling platelet count signals clotting, not bleeding.

Clinical recognition: the 4Ts

Suspect HIT using the 4Ts: the Timing (platelet fall typically 5–10 days after starting heparin, or faster on re-exposure), the degree of Thrombocytopenia (usually a fall of more than 50%, with a nadir rarely below 20 ×10⁹/L), new Thrombosis (venous or arterial), and the absence of another (oTher) explanation. Crucially, patients clot rather than bleed; bleeding is unusual, and the thrombosis can be limb- or life-threatening.

Diagnosis

Use the 4Ts score to gauge probability, then test. A PF4 immunoassay (anti-PF4/heparin antibodies) is highly sensitive—a negative result largely excludes HIT—but not specific, so a positive immunoassay in a high-probability patient is confirmed with a functional platelet-activation assay (such as the serotonin release assay), which is specific. Do not wait for confirmation to act if suspicion is high.

Management—and the traps

• Stop all heparin immediately: including flushes and LMWH—but note that stopping heparin alone is NOT sufficient treatment.
• Start a non-heparin anticoagulant: argatroban, fondaparinux, or a DOAC—because the patient remains intensely prothrombotic.
• Do NOT start warfarin until platelets recover: early warfarin can precipitate venous limb gangrene by dropping protein C; overlap and delay until the count normalizes.
• Avoid platelet transfusions: they add fuel to a prothrombotic fire and are reserved for serious bleeding only.
• Never re-expose: document the diagnosis and avoid all heparin in the future.

29Thrombotic Microangiopathies: TTP and HUStop ↑

Recognizing a TMA

The unifying triad is microangiopathic hemolytic anemia (anemia with schistocytes, high LDH, low haptoglobin), thrombocytopenia, and organ injury—without a coagulopathy. That last point is important: in TTP and HUS the PT, aPTT, and fibrinogen are typically normal, which separates them from disseminated intravascular coagulation. Any patient with schistocytes and a low platelet count needs urgent evaluation.

Thrombotic thrombocytopenic purpura (TTP)

TTP results from a severe deficiency of ADAMTS13, the enzyme that cleaves von Willebrand factor multimers—either congenital or, more often, from an acquired autoantibody. Without it, ultralarge VWF multimers accumulate and snare platelets into microthrombi, especially in the brain and heart. The classic pentad (microangiopathic hemolysis, thrombocytopenia, neurological changes, renal impairment, and fever) is often incomplete—do not wait for all five. Untreated TTP is frequently fatal, so the combination of microangiopathic hemolysis and thrombocytopenia without another explanation mandates urgent plasma exchange (which removes antibody and replaces ADAMTS13), with corticosteroids and, increasingly, caplacizumab and rituximab. Critically, do not transfuse platelets except for life-threatening bleeding—it can worsen the microthrombosis.

Hemolytic uremic syndrome (HUS)

HUS predominantly injures the kidney. Typical HUS follows infection with Shiga toxin–producing E. coli (often O157:H7), classically in a child after bloody diarrhea, and is largely supportive (the role of plasma exchange is limited). Atypical HUS arises from dysregulation of the complement system and is treated with complement blockade (eculizumab). The dominant feature in both is acute kidney injury rather than the neurological picture of TTP.

Distinguishing the look-alikes

The right product, safely matched, for the right patient

About Part VItop ↑

Transfusion is one of the most common hospital interventions and one of the most tightly regulated, because the consequences of error can be immediate and fatal. This chapter covers the components, the testing that makes a transfusion safe, the evidence-based thresholds for using them, and the reactions you must recognise.

30Transfusion Medicinetop ↑

Blood components

Whole blood is separated into components so each patient receives only what they need. Red cells raise oxygen-carrying capacity; platelets support primary hemostasis; plasma replaces coagulation factors; and cryoprecipitate concentrates fibrinogen.

Blood groups and pre-transfusion testing

The ABO system is the most important: individuals make naturally occurring antibodies against the A or B antigens they lack, so a mismatched red cell transfusion triggers immediate, complement-mediated intravascular hemolysis. Group O red cells lack A and B antigens and are the universal red cell donor; group AB plasma lacks anti-A and anti-B and is the universal plasma donor. The Rh system matters next—the D antigen is highly immunogenic, so Rh-negative patients (especially women of childbearing potential) should receive Rh-negative red cells to prevent sensitisation and hemolytic disease of the newborn.

Three tests make a red cell transfusion safe. ABO/Rh typing determines the patient's group; the antibody screen detects clinically significant antibodies to other red cell antigens (such as Kell, Kidd, and Duffy); and the crossmatch confirms compatibility between donor cells and recipient plasma before release.

When to transfuse: evidence-based thresholds

More blood is not better. Trials consistently favour a restrictive strategy: for most stable inpatients, transfuse red cells at a hemoglobin around 7 g/dL (a slightly higher threshold, around 8 g/dL, is used in active cardiac disease), and treat the patient and symptoms rather than a number. Platelets are given for bleeding with thrombocytopenia or to prevent it below low thresholds (and before procedures), but are generally avoided in ITP, TTP, and HIT unless bleeding is life-threatening. Fresh frozen plasma is for bleeding with a coagulopathy or urgent reversal, and cryoprecipitate for a low fibrinogen. In massive hemorrhage, products are given in balanced ratios.

Transfusion reactions

Recognizing reactions—and knowing which are emergencies—is core to safe practice.

Special products

Components can be modified for specific risks. Leukoreduction (now routine in many systems) removes white cells, reducing febrile reactions and CMV transmission. Irradiation inactivates donor lymphocytes to prevent transfusion-associated graft-versus-host disease in immunocompromised and certain other patients. Washing removes plasma proteins for patients with severe allergic reactions or IgA deficiency, and CMV-negative products are used for CMV-vulnerable patients such as some transplant recipients and neonates.

Afterwordtop ↑

This completes the benign hematology guide—from the foundations of how blood is made and measured, through the anemias, the non-malignant white cell disorders, bleeding and clotting, and finally transfusion. Used together with your lectures, textbooks, these chapters should make the difficult principles of hematology feel like a single connected way of thinking rather than a list of facts to memorize. The following companion malignant hematology guide covers the leukemias, lymphomas, myeloma, and the myeloid neoplasms.

Clonality, classification, and the questions that organize every blood cancer

About this guidetop ↑

This is the companion to the benign hematology handbook—a concise, high-yield student reference for the malignant disorders of blood: the leukemias, lymphomas, myeloma, and the myeloid neoplasms. Like its companion, it is a study aid created with AI assistance (Claude), not a publication or clinical reference, and should always be checked against your textbooks, current guidelines before any clinical use.

Part I builds the framework. Almost every blood cancer can be placed by answering a few questions—is it myeloid or lymphoid, acute or chronic, and how was it diagnosed—and managed by recognising a short list of emergencies. The disease-specific chapters in later parts then become applications of this framework. Each chapter keeps the same structure used throughout both guides: the big idea, the substance, pitfalls and pearls, a case, and a quick review.

1What Is a Hematologic Malignancy?top ↑

Cancer as a clonal genetic disease

Cancer begins at the level of the genes. Mutations disturb the normal controls on the cell cycle, differentiation, survival, and programmed cell death, so a cell proliferates when it should not and fails to mature or die. The defining feature of a hematologic malignancy is clonality—the tumor is the progeny of one transformed cell, all carrying the same genetic lesion. Some of these lesions are so characteristic that they name the disease and direct its treatment: the BCR-ABL fusion of chronic myeloid leukemia, the t(15;17) of acute promyelocytic leukemia, the JAK2 mutation of polycythemia vera. Known risk factors include ionizing radiation, certain chemicals (benzene) and prior chemotherapy, some viruses (EBV, HTLV-1, HIV), and inherited predisposition, though most cases are sporadic.

The two lineages and the two tempos

Blood cancers arise from one of two lineages. Myeloid neoplasms come from the cells that make red cells, platelets, and granulocytes; lymphoid neoplasms come from B, T, and NK cells. They also differ in tempo. Acute leukemias are dominated by immature blasts that proliferate rapidly and are fatal within weeks to months if untreated, but are potentially curable. Chronic disorders are made of more mature-appearing cells, behave indolently over years, and are often controlled rather than cured. A third axis is anatomical: the same lymphoid clone can circulate (leukemia), form a solid mass (lymphoma), or—when it is a plasma cell—flood the blood with a monoclonal protein (myeloma).

How they present

Hematologic malignancies declare themselves in a few recognizable ways. Marrow replacement causes failure of normal production—anemia (fatigue), neutropenia (infection), and thrombocytopenia (bleeding). Tissue infiltration produces lymphadenopathy, hepatosplenomegaly, or masses. Systemic disease causes the so-called B symptoms—fever, drenching night sweats, and unexplained weight loss. And many are found incidentally on a routine blood count. Recognizing these patterns is the first step toward the right test.

2Classification and the Diagnostic Toolkittop ↑

The four pillars of diagnosis

Morphology remains the starting point but is rarely sufficient alone. Flow cytometry assigns lineage and maturation by detecting clusters of differentiation (CD) markers. Cytogenetics reveals the recurrent translocations that define many entities, with FISH targeting specific rearrangements. Molecular testing detects point mutations and fusion transcripts, and—because it can find one tumor cell among many thousands—is the basis for monitoring minimal residual disease after treatment.

Getting the right sample

The diagnosis is only as good as the tissue. Peripheral blood with a film is the first look. The bone marrow aspirate (for morphology, flow, cytogenetics, and molecular tests) and trephine biopsy (for cellularity and architecture) are central to leukemias and staging. For lymphoma, an excisional lymph node biopsy is the gold standard, because the architecture of the whole node is needed—a fine-needle aspirate, which samples only scattered cells, is usually inadequate.

Why classification matters

Classification is not academic: it drives prognosis and therapy. The same morphological leukemia can be low or high risk depending on its cytogenetics, and specific lesions unlock targeted treatment—BCR-ABL is treated with a tyrosine kinase inhibitor, acute promyelocytic leukemia with all-trans retinoic acid, and CD20-positive B-cell lymphomas with rituximab. Increasingly, the molecular profile, not just the microscope, decides the plan.

3Approach to Lymphadenopathy and Organomegalytop ↑

Definitions and a structured differential

Lymphadenopathy is an abnormality in the size or consistency of one or more lymph nodes; it is localized when confined to one region and generalized when it involves two or more. A useful way to organize the causes is the mnemonic MIAMI: Malignancy (lymphoma, leukemia, metastatic carcinoma), Infection (viral, bacterial, TB, HIV), Autoimmune disease (lupus, rheumatoid arthritis), Miscellaneous/unusual (sarcoidosis, Castleman, Kikuchi), and Iatrogenic (drugs such as phenytoin). Most lymphadenopathy is reactive and self-limiting, but a minority signals serious disease.

Red flags for malignancy

• Hard, fixed, matted, or painless nodes (reactive nodes are usually tender and mobile).
• Size greater than about 2 cm, or persistent and progressively enlarging over weeks.
• Supraclavicular location—high malignancy risk at any age.
• Associated B symptoms (fever, drenching night sweats, weight loss) or hepatosplenomegaly.
• Older age and generalized lymphadenopathy with abnormal blood counts.

Workup

Begin with a careful history (duration, infectious exposures, constitutional symptoms, medications, risk factors) and examination of all node regions, the liver, and the spleen. Initial tests include a CBC and film, LDH (a surrogate for tumor bulk and turnover), and targeted infectious and autoimmune screens; imaging maps the extent of disease. When malignancy is suspected or nodes persist, an excisional lymph node biopsy is the definitive step—needed because lymphoma diagnosis depends on the architecture of the whole node, which a fine-needle aspirate cannot provide.

Organomegaly

Splenomegaly and hepatomegaly often accompany hematologic disease. A massively enlarged spleen suggests chronic myeloid leukemia or myelofibrosis; moderate enlargement accompanies lymphomas, CLL, and many non-malignant causes (infection, portal hypertension, hemolysis). The pattern of organ involvement, the blood counts, and the film together point toward the underlying diagnosis.

4Oncologic Emergencies and Principles of Treatmenttop ↑

Oncologic emergencies

Principles of treatment

Treatment of hematologic malignancy draws on four modalities, often combined. Cytotoxic chemotherapy kills rapidly dividing cells and remains the backbone of many regimens, at the cost of marrow suppression, mucositis, and tumor lysis. Targeted therapy exploits the specific lesion—tyrosine kinase inhibitors for BCR-ABL, JAK inhibitors for myelofibrosis, BCL-2 inhibitors, and many others—often with greater specificity and different side effects. Immunotherapy harnesses the immune system: monoclonal antibodies (rituximab against CD20), chimeric antigen receptor (CAR) T cells, and checkpoint inhibitors. Differentiation therapy is the elegant exception in acute promyelocytic leukemia, where all-trans retinoic acid forces the malignant cells to mature. Hematopoietic stem cell transplantation (Part IV) can be curative in selected patients. Underpinning all of these is supportive care—transfusion, infection prophylaxis, growth factors, and prevention of tumor lysis—which is often what makes intensive treatment survivable.

Too many blasts, too many mature cells, or a marrow that fails

5Acute Myeloid Leukemia (AML)top ↑

Pathophysiology and epidemiology

In AML, mutations both drive proliferation and block maturation, so immature blasts accumulate instead of becoming functional cells. The expanding clone crowds out normal hematopoiesis. AML is mainly a disease of older adults; it may arise de novo, evolve from a prior myelodysplastic or myeloproliferative disorder, or follow previous chemotherapy or radiation (therapy-related AML, which carries a worse prognosis).

Clinical features

Most features stem from marrow failure: anemia (fatigue, pallor), neutropenia (infection, including life-threatening sepsis), and thrombocytopenia (bruising, bleeding). Very high blast counts can cause leukostasis (breathlessness, confusion). Some subtypes infiltrate tissue—monocytic AML classically causes gum hypertrophy and skin lesions—and acute promyelocytic leukemia presents with disseminated intravascular coagulation and bleeding.

Diagnosis

The diagnosis rests on finding 20% or more myeloid blasts in the blood or marrow (or certain defining cytogenetic abnormalities at any blast count). Auer rods—pink rod-shaped inclusions—are pathognomonic of myeloid blasts. Flow cytometry confirms myeloid lineage (markers such as CD13, CD33, CD34, and myeloperoxidase), and cytogenetics and molecular testing define risk: favorable lesions include t(8;21), inv(16), and the t(15;17) of APL, whereas a complex karyotype and FLT3-ITD are adverse.

Treatment

Fit patients receive intensive induction chemotherapy—classically cytarabine plus an anthracycline (the "7+3" regimen)—aiming for remission, followed by consolidation that is risk-adapted: favorable-risk disease is consolidated with chemotherapy, while higher-risk disease is directed toward allogeneic stem cell transplantation. Targeted agents (FLT3 and IDH inhibitors) and lower-intensity options (hypomethylating agents with venetoclax) are used in selected and less fit patients. Intensive supportive care—transfusions, infection prophylaxis, and tumor lysis prevention—is essential throughout.

Acute promyelocytic leukemia (APL) — the curable emergency

APL is defined by the t(15;17) translocation producing the PML-RARA fusion, which arrests cells at the promyelocyte stage. It characteristically presents with DIC and severe bleeding. Crucially, the malignant cells can be forced to mature with all-trans retinoic acid (ATRA); combined with arsenic trioxide, this achieves very high cure rates—often without conventional chemotherapy. Because the early DIC is the main killer, ATRA should be started as soon as APL is suspected, before genetic confirmation.

6Chronic Myeloid Leukemia (CML)top ↑

Pathophysiology

The t(9;22) translocation fuses the BCR and ABL genes, producing a constitutively active tyrosine kinase that drives unregulated proliferation of the myeloid line. Untreated, CML evolves through three phases: a chronic phase (controllable, the usual presentation), an accelerated phase, and finally a blast crisis that behaves like an acute leukemia and is difficult to treat.

Clinical features

Many patients are diagnosed incidentally from a high white cell count. Symptoms, when present, include fatigue, weight loss, sweats, and abdominal fullness or early satiety from splenomegaly, which can be massive. The hypermetabolic clone may cause gout or priapism with very high counts.

Diagnosis

The blood shows a marked leukocytosis with the full spectrum of maturing myeloid cells (unlike acute leukemia, there is no "leukemic gap"), together with basophilia and often eosinophilia. The leukocyte alkaline phosphatase score is characteristically low (helping separate CML from a reactive leukemoid reaction). The diagnosis is confirmed by detecting BCR-ABL—by FISH or PCR—or the Philadelphia chromosome on karyotype.

Treatment

Tyrosine kinase inhibitors (imatinib and later-generation agents) are the cornerstone and have given most chronic-phase patients a near-normal life expectancy. Response is followed by measuring BCR-ABL transcript levels (molecular monitoring), with deep responses sometimes allowing treatment-free remission. Allogeneic transplantation is reserved for resistant disease or blast crisis. The key clinical discrimination is from a leukemoid reaction (a reactive neutrophilia), settled by the BCR-ABL test.

7Myeloproliferative Neoplasms (PV, ET, PMF)top ↑

Shared biology

These disorders share constitutive activation of the JAK-STAT growth pathway. The JAK2 V617F mutation is present in nearly all polycythemia vera and about half of essential thrombocythemia and primary myelofibrosis; CALR and MPL mutations account for many of the rest. The result is proliferation of one or more mature myeloid lineages without the normal regulatory brakes.

Polycythemia vera (PV)

PV is an increase in red cell mass (with variable rises in white cells and platelets), almost always JAK2-mutated. Patients are plethoric (ruddy), may have aquagenic pruritus (itching after a hot shower), headache, and splenomegaly, and are at high risk of arterial and venous thrombosis. A low serum erythropoietin supports the diagnosis and helps separate PV from secondary polycythemia (hypoxia, smoking, EPO-secreting tumors). Treatment is venesection to a target hematocrit, low-dose aspirin, and cytoreduction (hydroxyurea) in higher-risk patients.

Essential thrombocythemia (ET)

ET is a sustained, clonal increase in platelets, causing both thrombosis and—paradoxically, when counts are very high—bleeding from an acquired von Willebrand defect. It is partly a diagnosis of exclusion, since reactive thrombocytosis (iron deficiency, inflammation, infection, post-splenectomy) is far more common. Management is risk-adapted, using aspirin and adding cytoreduction (hydroxyurea) for higher-risk patients.

Primary myelofibrosis (PMF)

In PMF the marrow becomes progressively fibrosed, driving hematopoiesis out to the spleen and liver (extramedullary hematopoiesis). Patients develop cytopenias, constitutional symptoms, and often massive splenomegaly; the blood film is leukoerythroblastic (immature white and red precursors) with characteristic tear-drop red cells. JAK inhibitors (ruxolitinib) reduce spleen size and symptoms, and allogeneic transplantation—the only cure—is considered in higher-risk patients.

8Myelodysplastic Syndromes (MDS)top ↑

Pathophysiology

A mutated stem cell clone produces cells that mature abnormally (dysplasia) and undergo excessive apoptosis—so the marrow is typically hypercellular yet the blood counts are low (ineffective hematopoiesis). By definition the blast count is below 20% (at or above 20% the diagnosis becomes AML). Over time, accumulating mutations can drive transformation to acute leukemia.

Clinical features

MDS usually presents in an older adult with the consequences of cytopenias—most often a macrocytic or normocytic anemia causing fatigue, but also infections from neutropenia and bleeding from thrombocytopenia. Many patients are diagnosed after a persistent, unexplained anemia fails to respond to the usual treatments.

Diagnosis

The diagnosis requires persistent cytopenias together with morphological dysplasia in one or more lineages and fewer than 20% marrow blasts. The marrow shows dysplastic changes and may contain ring sideroblasts; cytogenetics are central both to diagnosis and prognosis (an isolated del(5q) is favorable and treatable, while monosomy 7 or a complex karyotype is adverse). Risk is formally graded with prognostic scores (such as the revised IPSS) that weigh blasts, cytogenetics, and the depth of cytopenias.

Treatment

Management is risk-adapted. Lower-risk disease is treated supportively—transfusions, erythropoiesis-stimulating agents, and iron chelation for transfusion overload—with lenalidomide especially effective for the del(5q) subtype. Higher-risk disease is treated with hypomethylating agents (azacitidine or decitabine) to delay progression, and allogeneic stem cell transplantation is the only curative option, offered to suitable fitter patients.

One lineage, many faces: blood, nodes, and marrow

9Acute Lymphoblastic Leukemia (ALL)top ↑

Pathophysiology and epidemiology

Immature lymphoid blasts (most often B-cell precursors, sometimes T-cell) accumulate in the marrow and crowd out normal hematopoiesis. ALL has a peak incidence in young children, with a second rise in older adults. Specific genetic lesions define risk: the Philadelphia chromosome (BCR-ABL), more common in adults, was historically adverse but is now targetable with tyrosine kinase inhibitors, while certain childhood cytogenetics are favorable.

Clinical features

Like AML, ALL causes marrow failure—anemia, infection, and bleeding—but lymphoid features are more prominent: lymphadenopathy, hepatosplenomegaly, and bone pain (children may limp or refuse to walk). T-cell ALL classically presents in an adolescent with a mediastinal mass. Central nervous system involvement can cause headaches, cranial nerve palsies, or meningism.

Diagnosis

The marrow shows lymphoid blasts (the 20% blast threshold applies as in AML). Flow cytometry establishes lineage and maturation (B-precursor markers such as CD19, CD10, TdT; or T-cell markers), distinguishing ALL from AML—a distinction that completely changes treatment. Cytogenetics and molecular testing (including BCR-ABL) refine risk and guide therapy. A lumbar puncture assesses CNS involvement.

Treatment

Treatment is prolonged and multiphase—induction, consolidation, and a long maintenance phase lasting two to three years—with mandatory CNS-directed therapy (intrathecal chemotherapy, sometimes cranial irradiation) because the CNS is a sanctuary site that systemic drugs penetrate poorly. Philadelphia-positive disease adds a tyrosine kinase inhibitor. Modern immunotherapies—blinatumomab and CAR T-cell therapy—have transformed relapsed and refractory disease, and allogeneic transplantation is used for high-risk patients. Cure rates exceed 85–90% in children but are lower in adults.

10Chronic Lymphocytic Leukemia (CLL)top ↑

Pathophysiology and presentation

A clone of mature-looking B cells accumulates in blood, marrow, nodes, and spleen, but these cells do not function normally. Most patients are older adults, and many are asymptomatic, diagnosed from a routine lymphocytosis. Others present with lymphadenopathy, splenomegaly, fatigue, or recurrent infections from immune compromise. (CLL and small lymphocytic lymphoma are the same disease, differing only in whether it is mainly in the blood or the nodes.)

Diagnosis

The blood shows a sustained mature lymphocytosis, and the film classically contains smudge (smear) cells—fragile lymphocytes ruptured during slide preparation. Flow cytometry is diagnostic, showing a characteristic clonal B-cell phenotype (CD19, CD5, and CD23 co-expression with weak surface immunoglobulin). Prognostic markers (IGHV mutation status, TP53/del(17p), and others) guide outlook and treatment choice.

Complications

The major complications reflect immune dysregulation: hypogammaglobulinemia with recurrent infections (the leading cause of death), and autoimmune cytopenias—particularly warm autoimmune hemolytic anemia and immune thrombocytopenia. Richter transformation is the uncommon but serious evolution of CLL into an aggressive large B-cell lymphoma, signaled by rapid nodal growth and systemic symptoms.

Treatment

Many patients are simply observed ("watch and wait"), since early treatment of asymptomatic disease does not prolong life. Treatment is reserved for progressive or symptomatic disease—bulky or symptomatic nodes, marrow failure, or significant cytopenias. Modern therapy is largely chemotherapy-free, using targeted oral agents: BTK inhibitors (ibrutinib and successors) and the BCL-2 inhibitor venetoclax, often with an anti-CD20 antibody. Autoimmune cytopenias are treated with corticosteroids.

11Hodgkin Lymphomatop ↑

Pathology

The defining cell is the Reed-Sternberg cell—a large, often binucleate B-cell-derived cell with prominent nucleoli (classically described as an "owl's eye" appearance), positive for CD15 and CD30. Remarkably, these malignant cells are sparse; most of the tumor is the reactive infiltrate of lymphocytes, eosinophils, and other cells they attract. Epstein-Barr virus is implicated in a proportion of cases.

Clinical features

Hodgkin lymphoma has a bimodal age distribution, peaking in young adults and again in older age. It typically presents with painless lymphadenopathy, often cervical or mediastinal, that spreads contiguously to adjacent nodal groups. B symptoms (fever, drenching night sweats, weight loss) carry prognostic weight; a classic but uncommon clue is pain in involved nodes after drinking alcohol. A large mediastinal mass may be found on chest imaging.

Diagnosis and staging

Diagnosis requires an excisional lymph node biopsy showing Reed-Sternberg cells in the typical background. Staging uses the Ann Arbor system (with PET-CT), classifying by the number and location of involved sites, whether disease is on one or both sides of the diaphragm, and the presence of B symptoms. The orderly, contiguous spread makes accurate staging especially meaningful here.

Treatment and outcome

Hodgkin lymphoma is highly curable. Treatment combines chemotherapy (the long-standing ABVD regimen and newer brentuximab-based or checkpoint-inhibitor regimens) with radiotherapy in selected cases, tailored to stage and risk. Because most patients are young and cured, a central concern is minimizing long-term toxicity—second cancers, cardiac disease, and infertility—from treatment. Relapsed disease may be salvaged with high-dose therapy and autologous transplantation.

12Non-Hodgkin Lymphoma (NHL)top ↑

A practical framework

There are many subtypes, but for a student the key is to separate aggressive from indolent disease, because the two behave and are managed in opposite ways.

Aggressive lymphomas

Diffuse large B-cell lymphoma is the most common NHL—a rapidly enlarging nodal or extranodal mass, frequently with B symptoms and a high LDH. It is treated promptly with immunochemotherapy (R-CHOP: rituximab plus chemotherapy) and is curable in a majority. Burkitt lymphoma is the extreme of aggression: an explosively proliferating tumor driven by a MYC translocation (t(8;14)), associated with EBV and endemic in parts of Africa, that carries a high risk of tumor lysis and demands immediate, intensive treatment.

Indolent lymphomas

Follicular lymphoma is the prototypical indolent NHL, typically driven by the t(14;18) translocation (overexpressing BCL-2, which blocks apoptosis). It usually presents with painless, waxing-and-waning lymphadenopathy and is widespread at diagnosis. Because it is slow-growing and incurable with standard therapy, asymptomatic patients are often observed, with treatment (anti-CD20-based) reserved for symptoms or organ compromise. A clinically important event is transformation to an aggressive lymphoma.

Diagnosis and the role of cell markers

As with all lymphomas, an excisional biopsy is required, with immunophenotyping to assign subtype (most are B-cell, CD20-positive—the target of rituximab) and cytogenetics to identify defining translocations. Staging uses PET-CT and marrow assessment. The expression of CD20 on most B-cell NHL is why anti-CD20 antibody therapy is so central.

13T-Cell Lymphomastop ↑

Where they fit

T-cell and NK-cell lymphomas are an uncommon, heterogeneous group — only about 10–15% of non-Hodgkin lymphomas in Western countries — arising from mature (post-thymic) T cells or natural killer cells. They are considered apart from the B-cell lymphomas of the previous chapter because they behave differently: most are aggressive, they respond less well to standard chemotherapy, and they generally carry a worse prognosis. (Precursor T-cell disease presents instead as T-lymphoblastic leukemia/lymphoma and is covered with ALL.)

Nodal (peripheral) T-cell lymphomas

Peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS) is the most common subtype — essentially a diagnosis of exclusion for aggressive nodal T-cell lymphomas that do not fit a defined entity. Angioimmunoblastic T-cell lymphoma (AITL) arises from follicular helper T cells and presents with generalized lymphadenopathy, fevers, skin rash, and polyclonal hypergammaglobulinemia. Anaplastic large-cell lymphoma (ALCL) is composed of large CD30-positive cells; the ALK-positive form occurs in younger patients and has a relatively good prognosis, whereas ALK-negative ALCL behaves more aggressively.

Extranodal and leukemic forms

Adult T-cell leukemia/lymphoma (ATLL) is caused by the retrovirus HTLV-1 (endemic in Japan, the Caribbean, and parts of Africa) and classically presents with hypercalcemia, lytic bone lesions, skin lesions, and circulating multilobated flower cells. Extranodal NK/T-cell lymphoma, nasal type is EBV-driven and produces a destructive midline nasal or palatal mass. Enteropathy-associated T-cell lymphoma (EATL) arises in the small bowel of patients with longstanding celiac disease.

Cutaneous T-cell lymphoma

In contrast to the aggressive nodal types, mycosis fungoides is an indolent cutaneous T-cell lymphoma that evolves slowly through patches, plaques, and finally tumors, with malignant CD4-positive T cells infiltrating the epidermis (Pautrier microabscesses). Its leukemic variant, Sezary syndrome, is defined by diffuse erythroderma, lymphadenopathy, and circulating Sezary cells with characteristic cerebriform nuclei.

Diagnosis

As with all lymphomas, an excisional biopsy with immunophenotyping is required. The cells express pan-T-cell markers (CD2, CD3, CD5, CD7) — often with aberrant loss of one of these as a clue to malignancy — and demonstrate a clonal T-cell receptor gene rearrangement. Useful subtype markers include CD30 (ALCL), ALK (ALK-positive ALCL), and EBV (NK/T-cell). Staging uses the same Ann Arbor system as other lymphomas, and HTLV-1 serology is checked when ATLL is suspected.

Treatment and prognosis

Most peripheral T-cell lymphomas are treated with anthracycline-based combination chemotherapy (CHOP or CHOEP), frequently followed by autologous stem-cell transplant in first remission because relapse is common. CD30-positive disease — notably ALCL — is treated with the antibody-drug conjugate brentuximab vedotin added to chemotherapy. Mycosis fungoides is managed with skin-directed therapy (topical steroids, phototherapy, local radiation), escalating to systemic agents only in advanced disease. Overall, with the important exceptions of ALK-positive ALCL and early mycosis fungoides, T-cell lymphomas have a poorer outlook than their B-cell counterparts.

14Multiple Myeloma and Plasma Cell Disorderstop ↑

Pathophysiology

A clone of malignant plasma cells expands in the bone marrow and secretes a monoclonal immunoglobulin (the paraprotein or M-protein), or just its light chains. The clone disrupts the body in several ways: it activates osteoclasts (lytic bone destruction and hypercalcemia), crowds the marrow (anemia), suppresses normal antibody production (immunodeficiency and infection), and its light chains damage the kidneys (cast nephropathy). This explains the whole clinical picture.

Clinical features — CRAB

• C — hyperCalcemia: from osteoclastic bone resorption; causes confusion, constipation, polyuria.
• R — Renal impairment: light-chain cast nephropathy, hypercalcemia, and dehydration.
• A — Anemia: marrow infiltration; fatigue and pallor; rouleaux on the film.
• B — Bone disease: lytic ("punched-out") lesions, pathological fractures, and bone pain, classically in the spine and skull.

Other features include recurrent infection (immunoparesis), hyperviscosity, and amyloidosis from light-chain deposition.

Diagnosis

The workup looks for the protein, the plasma cells, and the damage. Serum and urine protein electrophoresis with immunofixation detect and characterise the monoclonal protein (a sharp M-spike), and serum free light chains are measured. A bone marrow biopsy quantifies clonal plasma cells. Imaging (whole-body low-dose CT, MRI, or PET) identifies lytic lesions—note that the classic skeletal survey, and bone scans, may miss purely lytic disease. The diagnosis combines clonal marrow plasma cells with evidence of end-organ damage (the CRAB features) or specific biomarkers.

The spectrum and treatment

Myeloma is preceded by monoclonal gammopathy of undetermined significance (MGUS)—a common, asymptomatic monoclonal protein with no end-organ damage that carries a small annual risk of progression and is simply monitored—and by smoldering myeloma, an intermediate stage. Active myeloma is treated, not cured, with combinations of novel agents: proteasome inhibitors (bortezomib), immunomodulatory drugs (lenalidomide), and anti-CD38 antibodies (daratumumab), often followed by autologous stem cell transplantation in fit patients. Supportive care is essential—bisphosphonates for bone disease, hydration and prompt management of renal impairment and hypercalcemia, and infection prevention. Newer immunotherapies (CAR T-cells, bispecific antibodies) are changing the outlook in relapsed disease.

Transplant, supportive care, immunotherapy, and cellular therapy

15Hematopoietic Stem Cell Transplantationtop ↑

Two procedures, two logics

In an autologous transplant the patient's own stem cells are collected and frozen, then returned to rescue the marrow after a dose of chemotherapy that would otherwise be lethal—the graft is simply a rescue, and there is no immune benefit or graft-versus-host disease. In an allogeneic transplant the donor's stem cells engraft and rebuild a new immune system that can recognise and kill residual leukemia (the graft-versus-tumor effect); this immune power is the point of the procedure, but the same donor immunity can turn on the patient.

The transplant process

Donor matching for allogeneic transplant is based on human leukocyte antigen (HLA) typing—a matched sibling is ideal, with matched unrelated, haploidentical (half-matched family), and cord-blood donors as alternatives. The recipient first receives conditioning—chemotherapy with or without total body irradiation—to destroy residual disease and suppress the immune system so the graft can take. The stem cells are then infused and engraft over a couple of weeks, during which the patient is profoundly pancytopenic and at high risk.

Graft-versus-host disease (GVHD)

GVHD is the signature complication of allogeneic transplant: donor T cells recognise the recipient's tissues as foreign and attack them. Acute GVHD (early) targets the skin (rash), gut (diarrhoea), and liver (cholestasis); chronic GVHD (later) resembles an autoimmune disease affecting skin, mucosa, eyes, and other organs. It is prevented with immunosuppression (such as calcineurin inhibitors) and treated with corticosteroids. The flip side is the benefit: some graft-versus-host activity reflects the graft-versus-tumor effect that lowers relapse.

Other complications

Beyond GVHD, transplant patients face prolonged immunosuppression and infection (bacterial, fungal, and reactivation of viruses such as CMV), mucositis and organ toxicity from conditioning, veno-occlusive disease (sinusoidal obstruction) of the liver, graft failure, and—late—secondary malignancies and infertility. Intensive prophylaxis, monitoring, and supportive care span the whole course.

16Immunotherapytop ↑

Naked monoclonal antibodies

The simplest immunotherapies are antibodies aimed at a marker on the cancer cell. Binding flags the cell for destruction by the immune system (and can block growth signals). Rituximab, directed at CD20 on B cells, transformed the treatment of B-cell lymphomas and CLL and is the model for the class; daratumumab targets CD38 on myeloma plasma cells, and other antibodies target further antigens. Because CD20 is shared by normal B cells, these agents also deplete healthy B cells, contributing to infection risk.

Antibody-drug conjugates

An antibody-drug conjugate is a targeting antibody chemically linked to a potent cytotoxic payload—a guided missile that delivers chemotherapy directly to cells bearing the target antigen, sparing most normal tissue. Brentuximab vedotin (anti-CD30 linked to a microtubule poison) is used in Hodgkin lymphoma and CD30-positive disease; others target CD22 and CD33. The toxicity reflects both the antibody target and the released payload.

Bispecific antibodies

Bispecific antibodies bind two targets at once—typically a tumor antigen with one arm and a T-cell marker (CD3) with the other—physically bridging a cytotoxic T cell to the cancer cell and triggering it to kill. Blinatumomab links CD19 on B-ALL cells to CD3 on T cells and is effective in relapsed B-cell ALL; newer bispecifics target BCMA and other antigens in myeloma and lymphoma. Because they forcibly activate T cells, they can cause cytokine release syndrome.

Checkpoint inhibitors

Tumors can switch off T cells by engaging inhibitory "checkpoint" receptors (PD-1, CTLA-4). Checkpoint inhibitors block these brakes, unleashing the patient's own T cells against the tumor. In hematology their clearest role is in Hodgkin lymphoma, which is unusually sensitive. The trade-off is autoimmunity: by removing immune restraint, they cause immune-related adverse events—colitis, hepatitis, pneumonitis, dermatitis, and endocrinopathies—that are managed with corticosteroids.

17Cellular Therapytop ↑

What CAR T-cell therapy is

A chimeric antigen receptor (CAR) is a synthetic receptor that gives a T cell a new, made-to-order specificity. The patient's T cells are collected by apheresis, genetically engineered in the laboratory to express a CAR directed at a tumor antigen, expanded in number, and then infused back. Once inside the patient, these engineered T cells recognise the target antigen, activate, multiply, and kill antigen-bearing cells—and can persist as living, self-renewing therapy. The main targets are CD19 (for B-cell ALL and B-cell lymphomas) and BCMA (for multiple myeloma).

The two signature toxicities

• Cytokine release syndrome (CRS): the massive activation of CAR T cells releases a storm of cytokines, causing high fever, hypotension, and hypoxia that can progress to shock and organ failure. It is treated with the anti-IL-6 antibody tocilizumab and supportive care.
• Immune effector cell–associated neurotoxicity syndrome (ICANS): a distinct neurological toxicity—confusion, tremor, aphasia, and seizures—that is managed with corticosteroids.

Both typically occur in the days after infusion and require specialised inpatient monitoring. CAR T cells also deplete normal cells bearing the target (CD19 therapy causes B-cell aplasia and low immunoglobulins), and the lymphodepleting chemotherapy given before infusion adds cytopenias and infection risk.

Other cellular therapies

Cellular therapy is broader than CAR T cells. Allogeneic stem cell transplantation (Chapter 14) is itself a cellular therapy whose graft-versus-tumor effect is mediated by donor cells. A donor lymphocyte infusion gives extra donor T cells after allogeneic transplant to treat relapse by boosting that graft-versus-tumor effect. Natural killer (NK) cell therapies and tumor-infiltrating lymphocytes are further approaches, and the field is expanding rapidly toward off-the-shelf (allogeneic) and next-generation engineered cells.

Where it fits

Cellular therapies are generally used in relapsed or refractory disease that has failed standard treatment, where they can achieve remissions that were previously impossible. They are resource-intensive, require specialised centres, and demand careful patient selection, but they represent one of the most important advances in modern hematology.

18Principles of Supportive Caretop ↑

Tumor lysis syndrome

When a large, rapidly dividing tumor is treated, massive cell breakdown releases intracellular contents faster than the kidneys can clear them: potassium, phosphate, and uric acid rise while calcium falls, threatening arrhythmia and acute kidney injury. It is most dangerous in high-count leukemias and bulky, fast-growing lymphomas (Burkitt). Prevention is far better than cure—aggressive hydration plus uric-acid lowering with allopurinol (or rasburicase for high-risk patients) started before chemotherapy, with close electrolyte monitoring.

Febrile neutropenia

Fever in a neutropenic patient (ANC below 0.5 ×10⁹/L) is a medical emergency: without neutrophils, infection can progress to overwhelming sepsis within hours. The rule is immediate empirical broad-spectrum antibiotics after cultures, without waiting for results—do not delay for a source. Prophylactic antimicrobials and granulocyte colony-stimulating factor are used in selected high-risk settings, and any indwelling line is a suspect source.

Transfusion support

Patients with marrow failure or on intensive chemotherapy depend on transfusion. Red cells are given for symptomatic anemia using restrictive thresholds, and platelets are given for bleeding or prophylactically below low counts and before procedures. Two transfusion rules are specific to this population: cellular products should be irradiated for heavily immunosuppressed and transplant patients to prevent transfusion-associated graft-versus-host disease, and leukoreduced (and, where indicated, CMV-safe) products reduce febrile reactions and CMV transmission.

Growth factors and other support

Granulocyte colony-stimulating factor (G-CSF) shortens the duration of chemotherapy-induced neutropenia and is used to mobilise stem cells for collection; erythropoiesis-stimulating agents have a limited, selective role. Rounding out supportive care are antiemetics, mucositis care and nutrition, infection prophylaxis (antiviral, antifungal, and against Pneumocystis), and—because many regimens threaten fertility—fertility counselling before treatment begins. Throughout, clear communication and attention to the patient's quality of life matter as much as the cytotoxic plan.