Autoimmuine hemolytic anemias (AIHA) are classified into two groups of warm type and cold type according to the thermal properties of the anti-red cell autoantibody. A positive result of the antiglobulin test (DAT) confirms the presence of autoantibodies on red cells. DAT-negative AIHA are diagnosed by means of the elevation of red blood cell-associated IgG. The sera in low titer cold agglutinin disease show a low cold agglutinin titer but a high titer in the presence of bovine albumin. The antigenic specificity of warm reacting autoantibodies has been demonstrated, by using immunoblot and immunoprecipitation, such as Rh-related proteins, band 3, glycophorin A or Wrb antigen.