Non-vitamin K-dependent clotting factors during oral anticoagulant treatment.

The non-vitamin K-dependent coagulation factors fibrinogen, factor V, von Willebrand factor and factor XIII were measured in plasma of patients receiving oral anticoagulant treatment. Levels of fibrinogen, von Willebrand factor and factor XIII were above the upper normal limit in 60.0%, 58.6% and 53.4% of patients respectively. Factor V levels were below the lower normal limit in 56.3% of patients. Compared with a control group we found significant differences in the anticoagulated group for fibrinogen (P < 0.0001), factor V (P < 0.0001), von Willebrand factor (P < 0.0001) and factor XIII (P < 0.0001). It appears that the down-regulation of factors II, VII, IX and X during oral anticoagulation is accompanied by a subsequent up-regulation of fibrinogen, von Willebrand factor and factor XIII. This up-regulation or its absence could explain the thrombotic and bleeding complications seen in some patients on anticoagulant therapy and might also reduce the beneficial effect of oral anticoagulation in cardiovascular disease.