The Anti-Thrombin III (Antigenic) test is a blood test that measures the levels of a protein called anti-thrombin III (ATIII) in the blood. ATIII is a natural anticoagulant protein that helps regulate blood clotting by inhibiting the activity of certain clotting factors in the blood. This test is used to assess the risk of developing blood clots, especially in people with a history of recurrent thromboembolic events or a family history of clotting disorders. A low level of ATIII in the blood can increase the risk of abnormal blood clotting, leading to conditions such as deep vein thrombosis (DVT) or pulmonary embolism (PE). Conversely, a high level of ATIII in the blood may indicate a genetic deficiency or liver disease. The Anti-Thrombin III (Antigenic) test is a useful tool for assessing the risk of thrombotic events and for monitoring the effectiveness of anticoagulant therapy in people with clotting disorders. It involves taking a small sample of blood, which is then analyzed in a laboratory to determine the levels of ATIII.