Thrombin, a key enzyme in fibrin clot formation, converts the soluble fibrinogen to the insoluble fibrin. It is generated by the catalytic cleavage of its plasma precursor, prothrombin (factor II) and the activated Stuart factor (factor Xa). Thrombin also regulates homeostasis by activating the anticoagulant system of protein C and the inhibition of fibrinolysis. It is detected in the urine of patients with glomerular diseases.