Pathology
Haemolytic Anaemia
Haemolytic anaemia for MBBS and NEET-PG: intravascular and extravascular haemolysis, spherocytosis, G6PD deficiency, sickle cell, thalassaemia and immune haemolysis, mapped to NMC codes PA16.1 to PA16.7.
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Haemolytic Anaemia
Haemolytic anaemia for MBBS and NEET-PG: intravascular and extravascular haemolysis, spherocytosis, G6PD deficiency, sickle cell, thalassaemia and immune haemolysis, mapped to NMC codes PA16.1 to PA16.7.
This chapter covers the haemolytic anaemias, in which red cells are destroyed prematurely. It classifies them into hereditary and acquired, intravascular and extravascular, and details the blood pictures of spherocytosis, G6PD deficiency, sickle cell disease, thalassaemia and the immune and microangiopathic haemolytic anaemias.
High-yield: Haemolytic Anaemia
- Haemolytic anaemia is due to premature destruction of red cells with a compensatory increase in marrow production.
- The general features of haemolysis are raised reticulocytes, raised unconjugated bilirubin, raised lactate dehydrogenase and low haptoglobin.
- Extravascular haemolysis occurs in the spleen and causes splenomegaly and jaundice; intravascular haemolysis causes haemoglobinaemia and haemoglobinuria.
- Hereditary spherocytosis is a membrane defect (often spectrin or ankyrin) with spherocytes, raised osmotic fragility and a good response to splenectomy.
- Glucose-6-phosphate dehydrogenase deficiency causes episodic haemolysis on exposure to oxidant drugs, fava beans or infection, with bite cells and Heinz bodies.
- Sickle cell anaemia results from a single base substitution giving valine for glutamate at position 6 of the beta chain.
- Sickled cells cause vaso-occlusive crises, and the film shows sickle cells and target cells with features of hyposplenism.
- Beta thalassaemia major causes severe transfusion-dependent anaemia with marked microcytosis, target cells and skeletal changes.
- Autoimmune haemolytic anaemia is diagnosed by a positive direct Coombs (antiglobulin) test.
- Warm autoimmune haemolysis is IgG-mediated and shows spherocytes; cold agglutinin disease is IgM-mediated and worse in the cold.
- Microangiopathic haemolytic anaemia shows schistocytes (fragmented red cells) and occurs in DIC, TTP and HUS.
- Paroxysmal nocturnal haemoglobinuria is an acquired stem cell defect with complement-mediated intravascular haemolysis and thrombosis.
- Sickle cell trait is generally benign but can cause haematuria and renal papillary necrosis.
- The direct Coombs test detects antibody bound to red cells; the indirect Coombs test detects antibody in the serum.
Blood film clues in haemolytic anaemia
- **Spherocytes:** Hereditary spherocytosis and warm autoimmune haemolytic anaemia.
- **Bite cells / Heinz bodies:** G6PD deficiency after oxidant stress.
- **Sickle and target cells:** Sickle cell disease and thalassaemia.
- **Schistocytes:** Microangiopathic haemolysis: DIC, TTP and HUS.
NMC competencies in this chapter
- **PA16.1:** Definition and classification of haemolytic anaemia
- **PA16.2:** Pathogenesis, clinical features and haematologic indices of haemolytic anaemia
- **PA16.3:** Sickle cell anaemia and thalassaemia: pathogenesis, indices and blood picture
- **PA16.4:** Acquired haemolytic anaemia: aetiology, pathogenesis, indices and blood picture
- **PA16.5:** Peripheral blood picture in different haemolytic anaemias
- **PA16.6:** Prepare a peripheral blood smear and identify haemolytic anaemia
- **PA16.7:** Technique of cross-matching relevant to transfusion in haemolysis
Frequently Asked Questions
What laboratory features indicate haemolysis?
Raised reticulocytes, raised unconjugated bilirubin, raised lactate dehydrogenase and reduced haptoglobin, reflecting red cell destruction and marrow compensation.
What causes sickle cell anaemia?
A single base substitution giving valine for glutamate at position 6 of the beta-globin chain, which makes haemoglobin polymerise and distort the red cell when deoxygenated.
How is autoimmune haemolytic anaemia diagnosed?
By a positive direct Coombs test, which detects antibody bound to the surface of the patient's red cells.
What are schistocytes and where are they seen?
Fragmented red cells produced by mechanical shearing, seen in microangiopathic haemolytic anaemia such as DIC, TTP and HUS.
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