The threshold for TF- and FXa-initiated thrombin generation is lower in FVL plasma than in FV plasma and is dependent on TFPI. (A) A total of 0.05 to 1 pM TF or (B) 5 to 100 pM FXa initiated thrombin generation in plasma anticoagulated with citrate and CTI containing FV (black) or FVL (gray). Reactions were started by the addition of CaCl2 to plasma containing 4 μM PC:PE:PS in the presence (dashed line) or absence (solid line) of anti-K2 antibody (50 nM). At 0.05 pM TF or 5 pM FXa, no thrombin generation occurred unless TFPI activity was blocked. TF experiments were performed using 2 each of FV and FVL donors. FXa experiments were performed with 10 donors of each genotype. Representative thrombin generation curves from a single FV donor and a single FVL donor are shown (A-B).
