Acquired haemolytic anaemia
Autoimmune haemolytic anaemia
Acquired disorders resulting in haemolysis due to red cell autoantibodies.
Autoimmune haemolytic anaemia is subdivided according to the temperature at which the antibodies bind to the red cells:
· Warm autoimmune haemolytic anaemia: Antibodies bind best at 37◦ C
· Cold autoimmune haemolytic anaemia: Antibodies bind at lower temperatures, this type is further subdivided into cold haemagglutinin disease (CHAD) and paroxysmal cold haemoglobinuria.
· IgM or IgG antibodies are produced, which bind to red cells.
· IgM (and IgG which fully activates complement) cause lysis of cells within the vessel (intravascular haemolysis).
· IgG which only partially activate complement cause extravascular haemolysis with opsonised red cells either completely phagocytosed in the spleen or partially phagocytosed leading to the formation of spherocytes.
· The antibody coated red cells characteristic of autoimmune haemolytic anaemias are detected by the direct antiglobulin (Coomb’s) test (see Fig. 12.8).
The clinical features, specific investigations and management are summarised in Table 12.6.