The Inside Job
Hereditary hemolytic anemia — where the machine breaks by design: the membrane chassis, the enzyme engine, and the hemoglobin cargo.
Three parts, one survival bargain
To last 120 days squeezing through capillaries, the red cell was stripped of its brain and its factories. It survives entirely on a pre-built triad of stability — and hereditary hemolysis is simply one of these three failing.
1 · Chassis
Membrane skeleton — spectrin / ankyrin network. Durability & deformability.
2 · Engine
Metabolic enzymes — G6PD, pyruvate kinase. Energy & antioxidant defence.
3 · Cargo
Hemoglobin — sacrifices the nucleus & organelles to maximise O₂.
The trade-off: no nucleus, no ribosomes, no mitochondria means no repair. A born-in flaw in any one part shortens the whole journey.
Three families of defect
Each failing part gives a signature cell shape and a signature disease.
Hereditary spherocytosis: the rigid sphere
A weak membrane skeleton sheds fragments. As surface area is lost, the cell is forced into a sphere — the shape with the least surface for its volume — and a sphere can’t bend through the spleen.
Genetic defect
Mutation in spectrin, ankyrin, or band 3 destabilises the lipid bilayer.
Membrane shedding
Surface area is lost; the cell rounds into a rigid sphere.
Splenic conditioning
Rigid spheres can’t pass splenic sinusoids. Macrophages nip them until destruction — extravascular hemolysis.
Confirming HS: the osmotic fragility test
Jaundice, splenomegaly, a family history of anemia, and a negative Coombs. Spherocytes on the smear. To confirm, drop the cells into progressively weaker saline — the sphere, already near bursting, pops early. Drag the concentration.
| Reticulocytes | 8.5% |
| MCHC | 37 g/dL — dense |
| RDW-CV | 17.5% |
| Coombs | Negative |
| Bilirubin · LDH | High · High |
Two confirmatory tests
- Osmotic fragility — increased (cells burst in mild saline)
- EMA binding — decreased fluorescence (modern gold standard)
The smear shows spherocytes with no central pallor.
The HS curve is shifted toward higher saline — the cells lyse earlier. That is increased osmotic fragility.
G6PD: when oxidative defence fails
G6PD powers the only antioxidant line the red cell has. Remove it, and an oxidative hit goes unopposed — hemoglobin denatures and precipitates into Heinz bodies.
Triggers, and the cells they leave behind
The triggers
- Diet: fava beans (favism)
- Infection: acute illness, DKA — the most common trigger
- Drugs: antimalarials (primaquine), sulfonamides, nitrofurantoin
X-linked recessive. Hemolysis is episodic and intravascular.
Morphology gallery
Two ways hemoglobin fails
Normal HbA is two α + two β chains. A hemoglobinopathy is either a quantity problem or a quality problem.
Thalassemia · the quantity problem
Decreased synthesis of a globin chain → chain imbalance. The excess free chains precipitate and kill precursors — ineffective erythropoiesis.
Sickle cell · the quality problem
A point mutation (Glu→Val) in β-globin → structural failure. Hb polymerises under stress and deforms the cell.
The spectrum of β-globin loss
Reduced β chains → relative excess of α chains → precipitation in the marrow → cell death before release.
β-Thal minor (trait)
- Heterozygous
- Asymptomatic, mild microcytosis
- Key lab: HbA₂ > 3.5%
β-Thal major (Cooley’s)
- Homozygous (β-zero)
- Severe, transfusion-dependent
- “Chipmunk facies” from marrow expansion
- Risk: iron overload
The gene-deletion spectrum
Four α-globin genes; severity tracks how many are lost. Gold = intact, hatched-red = deleted.
Inset finding: the “golf-ball cell” — red cell stippled with Hb H inclusions.
One mutation, one switch
Glu→Val at position 6 of β-globin. Oxygenated, HbS stays soluble and the cell is round. Under stress — hypoxia, dehydration, acidosis — it polymerises into rigid fibers that sickle the cell. Flip the switch.
Case context: 20 yo male with musculoskeletal pain and splenomegaly. Autosomal recessive.
Acute crises & chronic damage
Acute vaso-occlusive crisis
- Pain crisis: bones, chest, extremities
- Acute chest syndrome: new infiltrate + fever — leading cause of death
- Splenic sequestration: rapid enlargement, Hb drop
Chronic sequelae
- Autosplenectomy → encapsulated-organism risk
- Renal failure
- Avascular necrosis
In sickle-cell disease: HbS > 90%, no HbA. The smear shows sickle cells.
Cornering a microcytic anemia
by exclusion
Clues in the blood
Confirm hemolysis, fork on the Coombs test, then let morphology name the cause.
Step 1 · confirm hemolysis
↑ reticulocytes · ↑ LDH · ↑ indirect bilirubin · ↓ haptoglobin.
Step 2 · the fork · Coombs (DAT)
Positive → autoimmune. Negative → hereditary — look at the smear.
| Smear finding | Confirmatory test | Diagnosis |
|---|---|---|
| Spherocyte | Osmotic fragility / EMA | HS |
| Bite cell | Enzyme assay | G6PD |
| Sickle cell | Electrophoresis | SCD |
| Target cell | Electrophoresis | Thalassemia |
Four things to carry
Architecture is destiny
The failing part (membrane, enzyme, cargo) dictates the cell shape and the presentation.
Rule out the common first
Microcytic? Rule out iron deficiency. Spherocytes? Check Coombs before calling it HS.
Management diverges
G6PD is avoidance of triggers. HS, thalassemia, SCD are about chronic organ damage.
The smear is the story
The peripheral smear is the most powerful, cost-effective first test.
“Look at the shape of the cell, and it will tell you where the machine broke.”
End of the Anemia series — three parts, from first principles to the peripheral smear.
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