TFPI prolongs the initiation of thrombin generation in plasma from patients with COVID-19. PFP from controls (n = 5) or patients with COVID-19 (n = 8) were first treated with heparinase and then incubated with either a neutralizing anti-TFPI antibody or control immunoglobulin G (IgG) for 30 minutes before triggering thrombin generation with TF and phospholipids. (A) Representative thrombin generation curves are presented, and the table shows comparisons of thrombin generation parameters between paired samples treated with anti-TFPI antibody vs control IgG. (B-D) Individual data points for lag time (B), T_max (C), and ETP (D) are presented as mean ± standard error for all except the lag time for controls are presented as median (interquartile range). Data presented as mean ± standard error were analyzed using the paired t test, and those with median (interquartile range) were analyzed using the Wilcoxon matched-pairs signed-rank test. ns, P > .05; ∗P < .05; ∗∗∗∗P < .0001. ns, not significant.