Plasma TFPIα is elevated in COVID-19. The isoform distribution of plasma TFPI was determined by measuring total TFPI (A) and TFPIα (B) by ELISA using a monoclonal anti-TFPI-K2 antibody for capture and biotinylated monoclonal anti-TFPI-K1 (total TFPI) or anti-TFPI-K3 (TFPIα) antibodies in controls (n = 29) and patients with COVID-19 (n = 44). Data are presented as median (interquartile range) and were analyzed using the Mann-Whitney U test.