[Suspected autoimmune coagulation factor IX deficiency difficult to diagnose due to concurrent lupus anticoagulant]

A woman in her 70s who was undergoing treatment for an overlap syndrome of autoimmune hepatitis and primary biliary cirrhosis developed persistent genital bleeding. Coagulation tests revealed a longer activated partial thromboplastin time, a 7% decrease in coagulation factor IX activity (FIX:C) and a FIX inhibitor (of 3 BU/ml). Lupus anticoagulant (LA), anticardiolipin antibody, and anti-β2 glycoprotein I antibody were positive, and the activated partial thromboplastin time cross-mixing test suggested the presence of LA. Additionally, all intrinsic coagulation factors decreased, but activity of all factors except FIX showed dilution linearity, which suggested a false decrease in activity due to LA. Although definitive diagnosis was difficult due to concurrent LA, this case was strongly suspected to be autoimmune coagulation FIX deficiency complicated by LA. Bypass therapy was not performed because the patient had no anemia and was positive for LA, and immunosuppressive therapy with prednisolone was initiated immediately. Eleven weeks after diagnosis, FIX:C was 41% and zFIX inhibitor was less than 1 BU/ml, leading to remission.