Antiglobulin reagent (Coombs') has been widely used for the diagnosis of autoimmune hemolytic anemia (AIHA) in a variety of species.

AIHA is an autoimmune disease characterized by antibody coated red blood cells that either lyse in the presence of complement, or are subject to phagocytosis by the liver and spleen, resulting in a severe anemia. A similar situation can occur in immune-mediated anemia. Instead of the antibody reacting with the red blood cell, antibody is directed toward a microbe (virus, mycoplasma, bacteria) or parasite that is associated with the red blood cells. An antibody coating results and the parasitized red cells are subject to lysis or phagocytosis in the same manner as the red cell in autoimmune hemolytic anemia