hematology and oncology
Autoimmune Hemolytic Anemia
Etiology of Autoimmune Hemolytic Anemia
Autoimmune hemolytic anemia is caused by Disorders extrinsic to the red blood cell . Warm antibody hemolytic anemia is the most common form of autoimmune hemolytic anemia (AIHA); it is more common among women. Autoantibodies in warm antibody hemolytic anemia react at temperatures≥37°C. Autoimmune hemolytic anemia may be classified as Primary (idiopathic) Secondary (occurring in association with an underlying disorder such as Systemic Lupus Erythematosus (SLE) , —see table Drugs That Can Cause Warm Antibody Hemolytic Anemia ) stimulate production of autoantibodies against Rh antigens ( In warm antibody hemolytic anemia, hemolysis occurs primarily in the spleen and is not due to direct lysis of RBCs. It is often severe and can be fatal. Most of the autoantibodies in warm antibody hemolytic anemia are IgG. Most are panagglutinins and have limited specificity. Cold agglutinin disease (cold antibody disease) is caused by autoantibodies that react at temperatures<37°C. Causes include Idiopathic (usually associated with a clonal B-cell population) Infections, especially mycoplasmal pneumonias or infectious mononucleosis (antibodies are directed against the I [mycoplasma] or i [Epstein Barr virus] antigens) Lymphoproliferative disorders (antibodies are usually directed against the I antigen) Infections tend to cause acute disease, whereas idiopathic disease (the common form in older adults) tends to be chronic. The hemolysis occurs largely in the extravascular mononuclear phagocyte system of the liver and spleen. The anemia is usually mild (hemoglobin>7.5 g/dL [70.5 g/L]). Autoantibodies in cold agglutinin disease are usually IgM. Antibody thermal amplitude is more important than its titer; the higher the temperature (ie, the closer to normal body temperature) at which these antibodies react with the RBC, the greater the hemolysis. Paroxysmal cold hemoglobinuria (PCH; Donath-Landsteiner syndrome) is a rare type of cold agglutinin disease. PCH is more common in children. Hemolysis results from exposure to cold, which may even be localized (eg, from drinking cold water, from washing hands in cold water). An IgG antibody binds to the P antigen on RBCs at low temperatures and causes intravascular hemolysis and hemoglobinuria after warming. It occurs most often after a nonspecific viral illness or in otherwise healthy patients, although it occurs in some patients with congenital or acquired Syphilis . The severity and rapidity of development of the anemia varies and may be fulminant. In children, this disease is often self-resolving. 