The Antithrombin III (AT III) test measures the level and activity of antithrombin, a natural anticoagulant that helps prevent excessive blood clotting. Deficiency in AT III increases the risk of deep vein thrombosis (DVT), pulmonary embolism (PE), and other clotting disorders.
✅ Evaluate unexplained or recurrent blood clots (thrombosis)
✅ Diagnose inherited or acquired antithrombin deficiency
✅ Monitor patients on anticoagulant therapy (e.g., heparin resistance)
✅ Assess clotting risk in high-risk conditions (e.g., pregnancy, surgery, or liver disease)
| AT III Level | Interpretation |
|---|---|
| 80-120% | Normal (adequate anticoagulation function) |
| 50-80% | Mild deficiency (may increase clotting risk, often acquired) |
| < 50% | Severe deficiency (high risk of thrombosis, often inherited) |
🔹 Low AT III levels suggest a higher risk of abnormal blood clotting (thrombophilia).
🔹 High AT III levels are rare but may occur with liver disease, nephrotic syndrome, or disseminated intravascular coagulation (DIC).
Inherited Antithrombin Deficiency (Type I & Type II) → Genetic disorder causing low AT III, leading to increased clotting risk.
Acquired AT III Deficiency → Caused by conditions like liver disease, nephrotic syndrome, DIC, chemotherapy, or prolonged heparin use.
Heparin Resistance → AT III deficiency can lead to poor response to heparin, requiring higher doses or alternative anticoagulants.
✔ D-Dimer → Detects recent clot formation.
✔ Protein C & Protein S Levels → Other natural anticoagulants; deficiencies also cause thrombosis.
✔ Factor V Leiden Mutation → Common genetic risk factor for clotting.
✔ Prothrombin Gene Mutation (G20210A) → Increases clot risk.
✔ Lupus Anticoagulant & Anticardiolipin Antibodies → Evaluate antiphospholipid syndrome (APS).
🔹 Investigate underlying cause (genetic testing for inherited deficiency, liver/kidney function tests for acquired causes).
🔹 Consider anticoagulation therapy (heparin, warfarin, or direct oral anticoagulants if clot risk is high).
🔹 Monitor closely during high-risk situations (e.g., surgery, pregnancy, immobility).