TFPI is a protease inhibitor that regulates the tissue factor (TF)-dependent pathway of blood coagulation. The coagulation process initiates with the formation of a factor VIIa-TF complex, which proteolytically activates additional proteases (factors IX and X) and ultimately leads to the formation of a fibrin clot. TFPI inhibits the activated factor X and VIIa-TF proteases in an autoregulatory loop. TFPI is glycosylated and predominantly found in the vascular endothelium and plasma in both free forms and complexed with plasma lipoproteins.