Autoimmune hemolytic anemia

Autoimmune hemolytic anemia (AIHA) occurs when a person's immune system produces antibodies directed against their own red blood cells (RBCs). These antibodies attach to red cells, causing them to break down (lyse), and reducing the number of oxygen-carrying red blood cells in circulation (anemia). The antibodies are usually directed against common red cell antigens, therefore they also bind to allogenic or transfused red cells and cause them to lyse. (ref). Autoimmune haemolytic anaemia can be caused by different types of antibodies with reactivity at different temperatures. The one caused by IgG antibodies is called warm-immune haemolytic anaemia and has an incidence of 5-10 cases per million whereas ‘cold agglutinin disease’ is caused by IgM antibodies with an incidence of 1-1.8 cases per million.

The terminology used in this disease is somewhat ambiguous. Although MeSH uses the term "autoimmune hemolytic anemia", some sources prefer the term "immunohemolytic anemia" so drug reactions can be included in this category. The National Cancer Institute considers "immunohemolytic anemia", "autoimmune hemolytic anemia", and "immune complex hemolytic anemia" to all be synonyms.