aPTT was first described by Langdell et al. It is employed to screen for abnormalities in the intrinsic (factors XII, XI, IX, VIII) and common coagulation pathway (Factors II, V, X and fibrinogen). aPTT may be ordered as part of a pre - surgical evaluation for bleeding tendencies, especially if the surgery carries an increased risk of blood loss or if the patient has a clinical history of bleeding. aPTT is moreover used for monitoring unfractionated heparin (UFH) therapy. A prolongation of the aPTT is also seen during oral anticoagulation therapy, after administration of thrombin inhibitors like hirudin, argatroban, or when circulating anticoagulants against a factor are present. Liver disease or consumptive coagulopathy may lead to prolonged aPTT results. Shortened aPTT results have been associated with hypercoagulability. The presence of non - specific inhibitors, such as lupus - anticoagulants, may prolong the aPTT.