The effect of factor X level on thrombin generation and the procoagulant effect of activated factor VII in a cell-based model of coagulation

We used a cell-based, in-vitro model of normal hemostasis and hemophilia to address the question of whether factor (F)X concentration affects the hemo static response to high-dose activated factor VII(FVIIa). Under conditions designed to mimic normal tissue factor-initiated hemostasis in vivo, we fou nd that only a very small amount of FX - equivalent to about 3% of the norm al plasma level - was required to support a 'normal' level of thrombin gene ration. This suggests that, under normal conditions in vivo, the level of F X does not significantly affect hemostatic function. By contrast, in experi ments designed to mimic the hemophilic condition, the level of FX had a sig nificant effect on the level of thrombin generated in the presence of high- dose FVIIa. This finding suggests that the plasma level of FX could affect the hemostatic response of hemophilic patients to high-dose FVIIa therapy. Blood Coagul Fibrinolysis 11 (suppl 1):S3-S7 (C) 2000 Lippincott Williams & Wilkins.