Hemorrhage in a cat caused by inhibition of factor XI (plasma thromboplastin antecedent).

A coagulation profile from a 5-year-old neutered male cat with severe epistaxis revealed an intrinsic coagulation defect characterized by prolonged activated partial thromboplastin time, with normal bleeding time, platelet count, and prothrombin time. Subsequent factor XI analyses, using bovine factor XI-deficient plasma, revealed factor XI deficiency. Hematologic and clinical studies on the cat failed to reveal an underlying disease process that might have resulted in acquired factor XI inhibition.