Reduced antithrombin III activity Antithrombin III deficiency UMLS:C0272375 Anti-thrombin III deficiency Antithrombin III (ATIII) inhibits the coagulation cascade by lysing thrombin and factor Xa. The defective inhibition of the coagulation cascade is associated with an increased risk of venous and arterial thrombosis. The physiological target proteases of antithrombin are those of the intrinsic pathway, namely the activated forms of Factor X, Factor IX, Factor XI, Factor XII, and, to a greater extent, Factor II (thrombin), and also the activated form of Factor VII (VIIa) from the the extrinsic pathway. SNOMEDCT_US:36351005 An abnormality of coagulation related to a decreased concentration of antithrombin-III. Decreased antithrombin III HP:0001976 Abnormality of the extrinsic pathway Abnormality of the intrinsic pathway