Thrombin generation is dependent on the initial prothrombin concentration.

Tissue factor–bearing cells were incubated with unactivated platelets, catalytic amounts of factor VIIa, calcium (3 mM), and plasma concentrations of factors IX, X, V, VIII, ATIII, and TFPI with increasing concentrations of prothrombin. At the times shown, samples were removed and assayed for the amount of thrombin as described in “Materials and methods.” Symbols: 0% (○), 1% (■), 10% (⋄), 50% (▵), 100% (●), 150% (▪), 200% (♦), and 300% (▴) of plasma levels. The absolute amounts of thrombin generated in each assay differed, depending on the procoagulant potential of the donor's platelets.33 Therefore, the data shown are representative of experiments with 8 different donors. (A) Thrombin generation profile from 0 to 60 minutes after the reaction start; (B) thrombin generation profile showing only the first 15 minutes of a reaction course. Panels A and B are from separate experiments using different donor platelets.