Tissue factor pathway inhibitor (TFPI) also known as Extrinsic pathway inhibitor (EPI), Lipoprotein - associated coagulation inhibitor (LACI), is a plasma proteinase inhibitor synthesized by vascular endothelial cells and part of it is associated with glycosaminoglycans of these cells. TFPI is a single-chain polypeptide which can reversibly inhibit Factor Xa (Xa) and Thrombin (Factor IIa). TFPI is a secreted protein with a N terminal acidic region, three Kunitz (K) domains separated with by two linker regions, and a C terminal basic region. The first K domain inhibits coagulation factor VIIa complexed to tissue factor (TF); The second K domain inhibits factor Xa; The third K domain binds to heparin; The C terminal basic region may have seve