[Occurrence of acquired factor V inhibitor during antibiotic therapy for a surgical wound infection].

Acquired factor V (FV) inhibitor is a rare disorder. Herein we report a case of an 82-year-old Japanese woman with FV inhibitor exhibiting a pseudo decline in the activities of the multiple coagulation factors. After rectal cancer surgery, she received antibiotic therapy for wound infection. As prothrombin and activated partial thromboplastin time was prolonged, heparin for atrial fibrillation was discontinued without improvement. Coagulation factor activity assays revealed deficiencies in II, V, VII, VIII, IX, X, XI, and XII factor activities; in particular, the FV activity was markedly decreased to <1%. The cross-mixing test findings revealed an inhibitor pattern, and multiple coagulation factor inhibitors were positive. The FV inhibitor level was high at 62 Bethesda U/ml. The patient exhibited no bleeding tendency with the prolonged wound infection without immunosuppressive therapy. The inhibitor disappeared four months after the onset.