Thrombomodulin is an endothelial cell surface glycoprotein that forms a 1:1 complex with thrombin. In this form, thrombin can activate approximately 1,000-fold more protein C than thrombin alone and does not activate coagulation factors, V and VIII, and platelets. Activated protein C inactivates factors Va and VIIIa. Thus thrombomodulin converts thrombin from a procoagulant protease to an anticoagulant. The soluble thrombomodulin present in human urine and plasma appears to represent a truncated form that lacks the transmembrane and cytoplasmic domains of tissue thrombomodulin. The plasma level of thrombomodulin has been used as a marker for endothelial injury in vivo. Elevated levels of soluble thrombomodulin were reported in the plasma from the patients with disseminated intravascular coagulation, adult respiratory distress syndrome (ARDS), and diabetes mellitus retinopathy.