Autoimmune hemolytic anemia (AIHA) due to the presence of warm agglutinins is almost always due to the presence of IgG antibodies that react with protein antigens on the red blood cell (RBC) surface at body temperature. For this reason, they are called "warm agglutinins" even though they seldom directly agglutinate the RBCs.
This topic review will discuss the clinical features and diagnosis of AIHA due to warm agglutinins [1,2]. Treatment of this disorder is discussed separately. (See "Treatment of autoimmune hemolytic anemia: Warm agglutinins".)
●AIHA is a frequent problem in patients with systemic lupus erythematosus, occurring in up to 10 percent of patients. This subject is discussed separately. (See "Hematologic manifestations of systemic lupus erythematosus in adults", section on 'Autoimmune hemolytic anemia'.)
●The pathogenesis, diagnosis, and treatment of AIHA associated with the presence of cold agglutinins is discussed separately. (See "Pathogenesis of autoimmune hemolytic anemia: Cold agglutinin disease" and "Clinical features and treatment of autoimmune hemolytic anemia: Cold agglutinins" and "Paroxysmal cold hemoglobinuria".)
A variety of factors may initiate the antibody production in warm agglutinin AIHA. This issue is discussed in detail separately. (See "Pathogenesis of autoimmune hemolytic anemia: Warm agglutinins and drugs", section on 'Genesis of antibody production'.) Reviewed briefly, most cases are idiopathic, in that no underlying disorder or direct cause can be found.