Plasma TFPI antigen and activity levels in groups of people with different FV levels. Total and free TFPI antigen levels were measured with commercial ELISAs, whereas TFPI activity levels were determined by a thrombin generation–based assay and expressed as an anti-TFPI ratio, as described in “Thrombin generation assays.” (A) Total TFPI antigen levels. (B) Free TFPI antigen levels. (C) TFPI activity levels. The horizontal bars represent the means of the respective groups. Probabilities of the Mann-Whitney Wilcoxon U test are indicated.