Comparison of TFPI_WT, TFPI-_ΔK3, and TFPI_K3P1 in FXa-induced coagulation of plasma. Assays were performed as described.²⁷  Briefly, a 50/50 mixture of TFPI and plasma was incubated at 37°C for 3 minutes before adding a second mixture containing FXa, CaCl₂, and cephalin, also preincubated at 37°C for 3 minutes, and the clotting time recorded using a fibrometer. Final concentrations for each reagent were TFPI (0-20nM), FXa (2nM), cephalin (25μM), and CaCl₂ (5mM). Assays were performed in duplicate. (A) Assay with PS-deficient plasma (B) Assay with pooled normal plasma. (C) Assay with PS-deficient plasma spiked with 200nM PS. ● indicates TFPI_WT; □, TFPI_K3P1; and ▵, TFPI-_ΔK3.