Effect of FV concentration on thrombin generation. Congenitally FV-deficient plasma was reconstituted with varying amounts of purified normal FV (A,C) or FV_Leiden (B,D). Thrombin generation after extrinsic activation of plasma in the absence (A-B) or presence (C-D) of 10 nM APC was measured as described in “Materials and methods.” ⋄ indicates 10% FV; □, 20% FV; ○, 60% FV; Δ, 100% FV; and ⋄, 120% FV.