Antithrombin III deficiency
Antithrombin III deficiency
Antithrombin III deficiency is an inherited cause of thrombophilia occurring in approximately 1:3,000 of the population. Inheritance is autosomal dominant.Role of antithrombin III
Antithrombin III (AT III) is a naturally occurring anticoagulant protein that helps regulate blood clotting. It inhibits several activated clotting factors, particularly:
- thrombin (factor IIa)
- factor Xa
- to a lesser extent: factors IXa, XIa, and XIIa
By neutralising these enzymes, antithrombin III prevents excessive thrombin generation and limits fibrin clot formation, maintaining the balance between coagulation and anticoagulation. Its activity is greatly enhanced by heparin, which accelerates the inhibition of thrombin and factor Xa.
Antithrombin III deficiency
Antithrombin III deficiency comprises a heterogeneous group of disorders, with some patients having a deficiency of normal antithrombin III whilst others produce abnormal antithrombin III
Features
- recurrent venous thromboses
- arterial thromboses do occur but are uncommon
Management
- thromboembolic events are treated with lifelong warfarinisation
- heparinisation during pregnancy
- as patients with antithrombin III deficiency have a degree of resistance to heparin anti-Xa levels should be monitored carefully to ensure adequate anticoagulation
- antithrombin III concentrates (often using during surgery or childbirth)
The table below shows the prevalence and relative risk of venous thromboembolism (VTE) of the different inherited thrombophilias:
| Condition | Prevalence | Relative risk of VTE |
|---|---|---|
| Factor V Leiden (heterozygous) | 5% | 4 |
| Prothrombin gene mutation (heterozygous) | 1.5% | 3 |
| Protein C deficiency | 0.3% | 10 |
| Protein S deficiency | 0.1% | 5-10 |
| Antithrombin III deficiency | 0.03 | 10-20 |
+PassMedicine Notes
Antithrombin III deficiency is an inherited cause of thrombophilia occurring in approximately 1:3,000 of the population. Inheritance is autosomal dominant.
Role of antithrombin III
Antithrombin III (AT III) is a naturally occurring anticoagulant protein that helps regulate blood clotting. It inhibits several activated clotting factors, particularly:- thrombin (factor IIa)
- factor Xa
- to a lesser extent: factors IXa, XIa, and XIIa
By neutralising these enzymes, antithrombin III prevents excessive thrombin generation and limits fibrin clot formation, maintaining the balance between coagulation and anticoagulation. Its activity is greatly enhanced by heparin, which accelerates the inhibition of thrombin and factor Xa.
Antithrombin III deficiency
Antithrombin III deficiency comprises a heterogeneous group of disorders, with some patients having a deficiency of normal antithrombin III whilst others produce abnormal antithrombin III
Features- recurrent venous thromboses
- arterial thromboses do occur but are uncommon
- thromboembolic events are treated with lifelong warfarinisation
- heparinisation during pregnancy
- as patients with antithrombin III deficiency have a degree of resistance to heparin anti-Xa levels should be monitored carefully to ensure adequate anticoagulation
- antithrombin III concentrates (often using during surgery or childbirth)
The table below shows the prevalence and relative risk of venous thromboembolism (VTE) of the different inherited thrombophilias:
Condition _ Prevalence _ Relative risk of VTE| Factor V Leiden (heterozygous) _ 5% _ 4| Prothrombin gene mutation (heterozygous) _ 1.5% _ 3| Protein C deficiency _ 0.3% _ 10| Protein S deficiency _ 0.1% _ 5-10| Antithrombin III deficiency_ 0.03 _ 10-20|