Warm reactive autoantibody positivity 2017-04-24T00:16:58Z Warm reactive antibodies react with the patients own RBCs and typically bind to all reagent or donor RBCs against which they are tested. However, they sometimes have specificity (absolute or relative) for a blood group antigen, most commonly a member of the Rh blood group system. Warm reactive autoantibodies are usually polyclonal IgG antibodies, although IgA or monomeric IgM antibodies are seen occasionally. Warm reactive autoantibodies are RBC-directed immune responses that are maximally reactive at 37 degrees C. Anti-erythrocyte autoantibody positivity