INCREASED SENSITIVITY OF FACTOR-IX TO PHENPROCOUMON AS A CAUSE OF BLEEDING IN A PATIENT WITH ANTIPHOSPHOLIPID ANTIBODY ASSOCIATED THROMBOSIS

We report one patient who presented with a spontaneous bleeding compli cation under phenprocoumon therapy. Oral anticoagulation was initiated due to deep-vein thrombosis which was attributed to an antiphospholip id antibody syndrome. Coagulation analysis revealed a strong and selec tive reduction of factor TX (F IX) activity to 1%, whereas the other v itamin K-dependent factors (II, VII, X), the prothrombin time and Inte rnational Normalized Ratio (INR) were within the therapeutic range. Af ter withdrawal of phenprocoumon, all vitamin K-dependent factors inclu ding F IX normalized. Because the patient suffered from a recurrence o f thrombotic events, he was re-exposed to phenprocoumon and the dispro portionate decline of F IX was observed again. These findings indicate an increased sensitivity of F IX to vitamin K antagonists, representi ng an uncommon mechanism associated with bleeding complications under oral anticoagulant treatment.