Effect of PS antibody on plasma thrombin generation. (A) Effect of PS antibody on plasma thrombin generation in 3 FIX-deficient commercial plasmas (George King, Stago, and HTI plasmas) represented as red (1), blue (2), and green (3) bars, respectively. The plasmas were incubated with 90 nM of FIX without (empty bar in each category) and with (filled bar in each category) a 450-nM PS antibody. Thrombin generation was measured in the presence of corn trypsin inhibitor (1 μM) and reagent B containing 0.4-pM tissue factor. The thrombin generation was initiated with a mixture of CaCl₂ and the fluorogenic substrate Z-Gly-Gly-Arg-AMC. The bars represent the peak thrombin that formed. Although many patients had recently received prophylactic FIX infusions, peak thrombin still increased in the presence of PS antibody. Student uncoupled t test was performed (P < .0001) to determine the level of significance as described.³⁴ (B-D) Effect of PS antibody on thrombin generation in patient plasmas (patients 1-11). Results are grouped according to severity of hemophilia, with panels B-D representing severe, mild, and moderate hemophilia, respectively. Patient 6, the single severe patient managed with an SHL product, is denoted by highlighting with a purple box. Patient plasmas were incubated with (blue curve) and without (red curve) PS antibody. Panel B P1 inset plot: effect of control (red - no TFPI antibody or PS antibody), TFPI antibody (green), and TFPI antibody + PS antibody (purple) on plasma thrombin generation.