Tissue Factor Pathway Inhibitor (TFPI) circulates in plasma as a complex with LDL>HDL>>VLDV. In plasma, TFPI is found in several forms: one at 36,000 kD, one at 43,000 kD, and the various truncated forms. This size heterogeneity appears in part to be the result of the formation of mixed disulfide complexes between TFPI and apolipoprotein AII. Approximately 10% of total TFPI is carried by platelets, which release TFPI once they are activated by thrombin. Thus, at the site of a wound, where platelets aggregate, elevated levels of TFPI are present. TFPI has dual inhibitory function (against factor Xa and factor VIIa/TF). This is consistent with the presence of multiple Kunitz-type domains: (Kunitz for factor VIIa/TF and Kunitz for factor Xa interaction).