Haemolytic anaemia
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Definition
Haemolytic anaemia refers to a reduction in red blood cell (RBC) lifespan due to premature destruction (haemolysis), leading to anaemia when bone marrow compensation is inadequate. It can be intravascular (within blood vessels) or extravascular (primarily in the spleen or liver).Classification
| Type | Subtypes / Examples |
|---|---|
| Hereditary | - Membrane defects: Hereditary spherocytosis, elliptocytosis - Enzyme defects: G6PD deficiency, Pyruvate kinase deficiency - Haemoglobinopathies: Sickle cell disease, Thalassaemia |
| Acquired | - Autoimmune (warm/cold antibody types – Coombs-positive) - Alloimmune: Haemolytic transfusion reaction, Haemolytic disease of the newborn - Microangiopathic: TTP, HUS, DIC - Infectious: Malaria - Chemical/drug-induced - Paroxysmal nocturnal haemoglobinuria (PNH) - Secondary to liver or renal disease |
Pathophysiology
Normal RBC lifespan ≈ 120 days; in haemolytic anaemia, destruction may occur in days. Erythropoietic hyperplasia and bone marrow expansion may compensate significantly before anaemia becomes evident.| Mechanism | Features |
|---|---|
| Extravascular | RBCs phagocytosed by macrophages in spleen/liver. Haem → protoporphyrin → bilirubin → bile. |
| Intravascular | RBCs lyse in circulation. Haemoglobin released into plasma → filtered by kidneys → haemoglobinuria. Toxic to renal tubules. |
Clinical features
- General signs of anaemia: fatigue, pallor, dyspnoea
- Jaundice (unconjugated hyperbilirubinaemia)
- Splenomegaly
- Pigment gallstones
- Dark urine (if intravascular)
- Frontal bossing / skeletal deformities (e.g. β-thalassaemia major)
- Leg ulcers (e.g. sickle cell anaemia)
- Parvovirus-induced aplastic crisis
- Megaloblastic anaemia due to folate depletion
Investigations
| Test | Finding |
|---|---|
| FBC | Low or normal Hb; ↑ MCV if reticulocytosis is high |
| Reticulocyte count | ↑ (unless marrow suppressed) |
| Peripheral smear | Polychromasia, anisopoikilocytosis, spherocytes, schistocytes |
| Unconjugated bilirubin | ↑ |
| LDH | ↑ (due to RBC breakdown) |
| Haptoglobin | ↓ (binds free haemoglobin; depleted in intravascular haemolysis) |
| Urine | ↑ Urobilinogen (extravascular); Haemoglobinuria, haemosiderinuria (intravascular) |
| Direct Coombs Test | Positive in autoimmune haemolytic anaemia |
| Bone marrow biopsy | Erythroid hyperplasia |
Important notes
- Marrow compensation can delay symptoms despite severe haemolysis.
- Intravascular haemolysis causes: transfusion reactions, G6PD deficiency, TTP/HUS/DIC, some autoimmune HA, PNH.
- Complications may include renal failure, gallstones, and folate deficiency.