Fibrinopeptide A is released from fibrinogen on thrombin action. It is useful as a tumor marker for circumscribed and disseminated gastric cancers. Higher levels have been found in nephrotic patients. Fibrinopeptide A is also used to detect hypercoagulable state in individuals with atrial fibrillation and in underlying activation of blood coagulation. In vivo, fibrinopeptide A is used as a marker to determine the rate of conversion of fibrinogen to fibrin by thrombin.