Tissue factor (TF) is a low molecular weight glycoprotein considered a major regulator of coagulation.1 Tissue factor pathway inhibitor (TFPI) appears to play a primary role in regulating TF-induced coagulation, as it is a potent inhibitor of activated factor VII/TF complexes. TFPI is expressed by the endothelium under normal physiologic conditions. The plasma concentration of TFPI is low, and only small amounts circulate in plasma as full-length molecule (free-TFPI).