Haemolytic anaemias are relatively infrequent. The more common of the congenital ones are hereditary spherocytosis and deficiencies of the red cell enzymes, pyruvate kinase and G6PD, although most cases of G6PD deficiency haemolyse only when the patient takes oxidant drugs such as sulphonamides or eats broad beans—'favism'.
Acquired haemolytic anaemias include those of the newborn due to maternal haemolytic blood group antibodies passing back through the placenta to the foetus, and adult anaemias due to drug toxicity or to acquired autoantibodies. About half of the latter are 'idiopathic' and half associated with non-Hodgkin's lymphomas, and the anaemia may be the presenting sign of lymphoma. Some of these antibodies are active only at cool temperatures—cold agglutinin disease; others act at body temperature and are the more potent cause of autoimmune haemolytic anaemia.
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