This gene encodes 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. The product of this gene inhibits the activated factor X and VIIa-TF proteases in an autoregulatory loop. The encoded protein is glycosylated and predominantly found in the vascular endothelium and plasma in both free forms and complexed with plasma lipoproteins. Several alternatively spliced transcript variants of this gene have been described, but the full-length nature of some of these variants has not been confirmed.