The Anti-Thrombin III test measures the level of antithrombin III (ATIII) in the blood, a protein that helps regulate blood clotting by inhibiting thrombin and other clotting factors. Low levels of antithrombin III can increase the risk of abnormal clotting, leading to conditions like deep vein thrombosis (DVT) or pulmonary embolism. This test is used to assess the risk of clotting disorders, monitor patients with known ATIII deficiencies, and guide treatment for individuals on anticoagulants. A blood sample is required for this test.