Haemolytic Anaemia: Patterns and Laboratory Clues

Key points

• • Haemolysis shortens red cell survival, and a healthy marrow answers with reticulocytosis.
• • The common laboratory signature is a raised reticulocyte count, raised unconjugated bilirubin, raised lactate dehydrogenase and a low or absent haptoglobin.
• • Intravascular haemolysis adds haemoglobinaemia, haemoglobinuria and haemosiderinuria, as seen in ABO-incompatible transfusion, paroxysmal nocturnal haemoglobinuria and microangiopathic processes.
• • Extravascular haemolysis happens in splenic macrophages and shows as jaundice with splenomegaly, as in hereditary spherocytosis and warm autoimmune haemolysis.
• • A positive direct antiglobulin (Coombs) test supports immune haemolysis, while a negative test makes it less likely but does not absolutely exclude it.
• • Blood film clues: spherocytes in hereditary spherocytosis and warm autoimmune haemolysis, bite cells with Heinz bodies in G6PD deficiency, schistocytes in microangiopathy, sickle cells in HbS disease and target cells in thalassaemia.