Introduction Autoantibody against a coagulation factor Anti-Factor VIII is the most common recall factor VIII is deficient in hemophilia A Presentation Symptoms hemarthroses intramuscular bleeding GI bleeding excessive bleeding in response to minor trauma indistinguishable from hemophilia Evaluation Labs ↑ PTT normal PT, bleeding time Mixing studies supplied factor does not result in clot formation antibody inhibits supplied factors used to distinguish from hemophilia, which would clot when supplied normal plasma