Clinical: Haematology - Autoimmune haemolytic anaemia.

This condition may be primary or secondary to infection or lymphoma, says Professor David Roberts.

Autoimmune haemolytic anaemia (AIHA) is due to shortened red cell survival that is not fully compensated for by increased bone marrow production. It is caused by binding of autoantibodies to red cell membrane antigens and the destruction or removal of red cells.

There are two main types. Warm AIHA (80-90% of cases) is usually caused by IgG autoantibodies binding to red cells at 37 degsC, activating complement and causing removal of cells by macrophages (known as extravascular haemolysis).

Cold AIHA (10-15% of cases) is caused by IgM or occasionally IgG autoantibodies that bind strongly to red cells at <37 degsC, giving rise predominantly to intravascular haemolysis with or without acrocyanosis (purplish discoloration of the distal limbs, fingers and toes) due to occlusion of peripheral blood vessels in the cold.

Two forms of cold AIHA are cold haemagglutinin disease (CHAD) and paroxysmal cold haemoglobinuria (PCH), which is caused by antibody binding to erythrocytes in the cold, but activating complement and causing …