- Overview
- Antithrombin (AT), also known as AT III or heparin cofactor I, is a natural anticoagulant.
- Inhibits thrombin (factor IIa), factor Xa, and other serine proteases.
- Hereditary AT deficiency is autosomal dominant with variable penetrance.
- Rare condition: 0.02–0.2% in the general population.
- Acquired conditions can lower AT levels, but clinical significance is often limited.
- Need antithrombin for platelets to respond to heparin
- So can present with Heparin resistance
- Clinical
- Confers a higher risk of thrombosis compared to other hereditary thrombophilias.
- Presentation varies from no VTE to life-threatening VTE in childhood, early adulthood, or during pregnancy.
- May present as kidney disease or heparin resistance
- Diagnosis
- Best initial test: Plasma AT activity (AT-heparin cofactor assay).
- Perform testing post-acute VTE and off anticoagulation therapy.
- Management
- Anticoagulation: Standard therapeutic anticoagulation for VTE; prophylaxis in high-risk situations (e.g., pregnancy, surgery).
- AT Concentrate: Replacement therapy using human plasma-derived or recombinant AT in select cases.