Plasma levels of protein C and vitamin K-dependent coagulation factors in patients on long-term oral anticoagulant therapy.

Plasma levels of protein C (PC) and vitamin K-dependent coagulation factors (factors II, VII, IX and X) were measured in 100 specimens from patients on long-term warfarin therapy. Both activities and antigens of these coagulation factors were decreased, depending on the thrombotest values. Factor II activity/antigen ratio and factor X activity/antigen ratio were correlated well with thrombotest values, indicating that the concentration of inactive molecules (PIVKAs) relative to normal proteins increases with increasing intensity of anticoagulation. Although PC antigen (PC:Ag) was also decreased, the ratios between PC:Ag and vitamin K-dependent coagulation factor antigens remained constant, being independent of the intensity of warfarin therapy. These findings indicate that long-term oral anticoagulant therapy results in the suppression of the synthesis of both vitamin K-dependent coagulation factors and PC, but the production of the coagulant and anticoagulant proteins is well-balanced.