Inhibition of plasma TFPI reduces the lag time for initiation of thrombin generation to a greater extent in FV plasma than in FVL plasma. Plasma thrombin generation assays were initiated with either (A-B) 100 pM, (C) 20 pM, or (D-F) also 100 pM FXa. Assays were performed in the absence or presence of (A) 1 nM TFPIα, (B-C) 50 nM anti-K2, (D) 50 nM anti-K3C, (E) 50 nM anti-K1, or (F) 1 μM LIKTKRKRKK. Shown are the changes in lag time, relative to the untreated plasma control (n = 10 for each genotype). The boxes represent the 25th to 75th percentile; the whiskers represent minimum and maximum values; and the lines represent the median values. Het, heterozygous.