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Pathogenesis of autoimmune hemolytic anemia: Warm agglutinins and drugs

Stanley L Schrier, MD
Carlo Brugnara, MD
Section Editor
William C Mentzer, MD
Deputy Editor
Jennifer S Tirnauer, MD


One of the most common causes of acquired hemolytic anemia is immunologic destruction of red blood cells (RBCs) mediated by autoantibodies directed against antigens on the patient's RBCs. The clinical manifestations of this group of diseases, called autoimmune hemolytic anemia (AIHA), depend greatly on the type of antibody that is produced by the abnormal immune reaction.

This topic review will discuss the mechanisms underlying AIHA due to warm agglutinins and drugs. The diagnosis and treatment of this disorder and issues related to cold agglutinins and paroxysmal cold hemoglobinuria are discussed separately. (See "Warm autoimmune hemolytic anemia: Clinical features and diagnosis" and "Warm autoimmune hemolytic anemia: Treatment" and "Pathogenesis of autoimmune hemolytic anemia: Cold agglutinin disease" and "Paroxysmal cold hemoglobinuria".)


In general, antibodies of two major types, each with specific characteristics, are produced in AIHA:

IgG antibodies which generally react with protein antigens on the RBC surface at body temperature. For this reason, they are called "warm agglutinins" even though they seldom directly agglutinate the RBCs. Rarely, IgM antibodies have these reaction characteristics and readily agglutinate red cells.

IgM antibodies which generally react with polysaccharide antigens on the RBC surface only at temperatures below that of the core temperature of the body. They are therefore called "cold agglutinins." Rarely, IgG antibodies have these reaction characteristics.

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Literature review current through: Nov 2017. | This topic last updated: Sep 26, 2017.
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