Baseline TFPI concentration is associated with delayed initiation of thrombin generation in COVID-19 plasma. (A) PFP from patients with COVID-19 (red squares) and healthy controls (blue circles) was treated with heparinase, and thrombin generation was triggered by 1 pM TF and phospholipids. Data were collected for lag time, T_max, thrombin peak, velocity index, and ETP. Representative thrombin generation curves are presented, and the table shows comparisons of thrombin generation parameters between controls (n = 21) and patients with COVID-19 (n = 40). Data showing normal distribution are presented as mean ± standard error and were analyzed using the unpaired t test. Data not showing normal distribution are presented as median (interquartile range) and were analyzed using the Mann-Whitney U test. (B) Total TFPI levels in plasma from healthy controls (blue circles; n = 22) and patients with COVID-19 (red squares; n = 62) were measured by ELISA. Data are shown as fold change from the mean value of healthy controls, presented as mean ± standard error, and analyzed using the unpaired t test. ∗∗∗∗P < .0001. (C-G) Simple linear regression analysis of thrombin generation potential parameters and TFPI in COVID-19 plasma (n = 31).