Acquired hemophilia masked by warfarin therapy

People without hemophilia but with autoantibodies specifically directed aga inst the procoagulant activity of factor VIII are known to have acquired he mophilia. The bleeding diathesis in these patients is often severe and life -threatening. The definite. laboratory diagnosis of this disorder includes demonstration of low factor VIII levels in plasma with a high titer of fact or VIII inhibitors, but the initial suspicion for its presence should rise in view of a prolonged partial thromboblastin time (PTT) and a normal proth rombin time associated with an acquired bleeding disorder. Oral anticoagula nt treatment is known to prolong PTT as well, and the merger of these 2 sit uations may cause delayed diagnosis of acquired hemophilia with devastating consequences. We describe here the first reported case of acquired hemophi lia diagnosed in a patient treated with warfarin. In such patients prolonge d PTT may be ascribed to warfarin therapy rather than to acquired hemophili a, thus causing a dangerous delay in diagnosis.