This test measures the activity of Antithrombin III (AT III), a protein that naturally inhibits several enzymes in the coagulation cascade, including thrombin and factor Xa.
Diagnostic Value: Low AT III activity can indicate antithrombin deficiency, which leads to an increased risk of abnormal clot formation.
Clinical Significance: AT III deficiency may be inherited or acquired (from liver disease, nephrotic syndrome, or prolonged heparin therapy). Testing is often ordered when blood clots occur at a young age or in unusual sites.
Symptom Correlation: Patients may present with leg swelling, pain, or pulmonary embolism due to clot formation.
Because it reflects one of the body’s main natural anticoagulant systems, the AT III Activity test is crucial for identifying and managing thrombophilia.