Expansion
Raised reticulocytes, bilirubin and LDH with low haptoglobin
Expansion
Markers of increased red cell destruction
- Unconjugated bilirubin raised, giving prehepatic jaundice
- LDH raised, released from lysed cells
- Haptoglobin low or absent, consumed by binding free haemoglobin
- Urinary urobilinogen raised; haemosiderinuria in chronic intravascular haemolysis
Markers of increased production
- Reticulocytosis, with polychromasia on the film
Then classify
- Direct antiglobulin (Coombs) test: positive means immune haemolysis, warm (IgG, often idiopathic, lupus, lymphoma, methyldopa) or cold (IgM, Mycoplasma, infectious mononucleosis)
- Negative Coombs: consider membrane defects (spherocytosis), enzyme defects (G6PD, pyruvate kinase), haemoglobinopathies, mechanical causes (prosthetic valves, microangiopathy), infection (malaria) and paroxysmal nocturnal haemoglobinuria
The blood film is often diagnostic: spherocytes, sickle cells, bite cells and Heinz bodies in G6PD, schistocytes in microangiopathy, and malarial parasites.
Intravascular haemolysis causes haemoglobinuria and profound haptoglobin depletion; extravascular haemolysis in the spleen causes splenomegaly and jaundice.