An antibody that reacts against red blood cells of the same species. This is a term rarely used by blood bankers, but clinicians may use it occasionally. You may also see it used in the scientific literature, especially older articles (some of those papers used the term in place of “isohemagglutinin“). Most use isoantibody synonymously with “alloantibody,” but technically, “autoantibodies” could be included within the definition above. Confused yet? Just stick with “alloantibody”and “autoantibody” and most everyone will be happy!