Antithrombin III deficiency
Medical condition
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Related on Lably
Through Genetic disorder and Dominance (genetics)
The prevalence of antithrombin deficiency is estimated at ~0.02 to 0.2% of the general population, and 1-5% of patients with venous thromboembolism. There is an elevated risk of thrombosis, whereby 50% patients with AT deficiency were found to have venous thromboembolism by age 50.
Presentation
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Diagnosis
A clinical suspicion for antithrombin deficiency can be made in patients with: 1. recurrent venous thromboembolic disease, 2. childhood thrombosis, 3. thrombosis in pregnancy. Testing for antithrombin activity can confirm deficiency if the levels are less than 70%. Deficiency can result from genetic predisposition or from acquired causes such as: acute thrombosis, disseminated intravascular coagulopathy, liver disease, nephrotic syndrome, L-asparaginase, oral contraception, or estrogens. Genetic testing for abnormalities of the SERPINC1 gene can be done to evaluate further.
Management
In patients with antithrombin deficiency, they may develop resistance to unfractionated heparin, especially with continuous infusions. If large quantities of unfractionated heparin are required e.g. greater than 35000 units per day, this would point towards resistance. Antithrombin concentrates have been used, though with risk of bleeding at large doses of unfractionated heparin. Low molecular weight heparin at full weight based dosing is effective; however, measurements of peak anti-Xa levels may not reflect anticoagulant effect. Vitamin K antagonists, and direct oral anticoagulants, including anti-Xa inhibitors and thrombin inhibitors have also been used, though data is limited.