Autoimmune hemolytic anemia (AIHA) due to the presence of warm agglutinins is almost always due to 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 manifestations 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 also a frequent problem in patients with systemic lupus erythematosus (SLE), 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'.)
A variety of factors may initiate the antibody production in warm agglutinin AIHA. This issue is discussed in detail elsewhere. (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.
Underlying causes — Underlying causes or conditions that may be associated with AIHA include the following: