[Autoimmune haemolytic anemias]

Autoimmune haemolytic anemia (AIHA) is defined as the immune-mediated destruction of red blood cells. In most cases, antibodies that target surface antigens on erythrocytes lead to their premature degradation in the spleen or, less commonly, in the liver. The term includes a heterogenous group of diseases, which differ largely in pathophysiology and treatment. The two most common entities are warm AIHA and cold AIHA. Diagnostic testing involves the analysis of haemolytic markers like lactate dehydrogenase, haptoglobin and unconjugated bilirubin as well as a hemoglobin and reticulocytes. In case of a haemolytic anemia, further testing like a blood smear and a direct antiglobulin test should follow. As diagnostic testing and treatment of AIHA are complex, affected patients should always be referred to a hematologist.In warm AIHA, mainly IgG autoantibodies bind to their antigen on the erythrocyte surface at body temperature, leading to their premature destruction in the spleen. First line treatment options include the administration of steroids which mitigate the destruction of red blood cells by macrophages in the spleen. In contrast, IgM autoantibodies in cold AIHA lead to intravasal agglutination of erythrocytes and complement activation. The IgM antibodies have their highest affinity below body temperature which is why patients experience symptoms mainly in cold-exposed body areas. Although the IgM antibodies dissolve at body temperature, the complement-loaded erythrocytes are destroyed in the liver. Therapeutic options include protection from cold and immunosuppressive agents or complement inhibition.