[Autoimmune acquired factor V deficiency developing after thoracic aortic aneurysm repair]

Acquired factor V deficiency is a rare bleeding disorder caused by autoantibodies against factor V, resulting in marked reduction of activity and bleeding tendency.

We report the case of an 81-year-old man who developed acquired factor V deficiency after total arch replacement and open stent grafting for a thoracic aortic aneurysm. Postoperatively, despite the absence of bleeding tendency, both prothrombin time (PT) and activated partial thromboplastin time (APTT) were markedly prolonged. Factor assays revealed factor V activity <3%, and a factor V inhibitor was detected (1 BU/ml). A cross-mixing test indicated a pattern of factor deficiency, suggesting the involvement of clearance-facilitating antibodies in addition to neutralizing antibodies.

Acquired factor V deficiency is often associated with surgery, transfusions, or antibiotics. Although rare, it should be considered in patients with unexplained prolongation of PT and APTT. Cross-mixing tests may mimic factor deficiency patterns when clearance-facilitating antibodies are present, requiring careful interpretation. Immunosuppressive therapy including corticosteroids, cyclophosphamide, or rituximab has been reported effective, while bleeding episodes may be managed with plasma or bypassing agents.

This case emphasizes the importance of considering acquired factor V deficiency in the differential diagnosis of postoperative coagulopathy with unexplained prolongation of PT and APTT.