[A case of acquired hemophilia A discovered by right renal bleeding].

An 81-year-old man was referred to our hospital with a chief complaint of asymptomatic macrohematuria. Cystoscopy revealed bleeding from the right ureteral orifice. Various examinations, including ureteroscopy, failed to find any abnormalities. As gingival bleeding followed the macrochematuria, further examinations of blood coagulatory function were undertaken. Decreased factor VIII coagulant activity accompanied by the presence of factor VIII inhibitor was revealed, leading to a final diagnosis of acquired hemophilia A. Macrohematuria and gingival bleeding immediately disappeared with oral administration of prednisolone at 30 mg per day, and the titer of factor VIII inhibitor decreased to an undetectable level by the 45th day of treatment. We emphasized the importance of blood coagulation testing in the examination of patients with macrohematuria.