Genetic Thrombosis Testing Recommendations

Indications for Testing

Genetic thrombophilia testing is recommended for patients under age 50 with any venous thrombosis, as stated by the American College of Medical Genetics, 2, 4
Testing is also recommended for patients with venous thrombosis in unusual sites, such as hepatic, mesenteric, or cerebral veins, 2, 5
Patients with recurrent venous thrombosis should undergo genetic thrombophilia testing, 2, 6
A strong family history of thrombotic disease is an indication for genetic thrombophilia testing, 2, 7
Pregnant women or women taking oral contraceptives who develop venous thrombosis should be tested, 2, 3

Either direct DNA-based genotyping or a factor V Leiden-specific functional assay is recommended for testing, 4, 5
Patients who test positive by functional assay should have confirmatory DNA testing to distinguish heterozygotes from homozygotes, 4, 5
Consider testing for other thrombophilias, particularly prothrombin 20210A mutation, when testing for factor V Leiden, 10

Factor V Leiden homozygotes should be considered for lifetime antithrombotic prophylaxis after a thrombotic event, 7, 8
Patients heterozygous for both factor V Leiden and prothrombin 20210A mutation have high recurrence risk and should be considered for indefinite anticoagulation, 8
Knowledge of factor V Leiden status in asymptomatic relatives can guide antithrombotic prophylaxis during high-risk periods, particularly postpartum, 7, 8

The risk of major bleeding with chronic warfarin therapy may reach 8% per year, requiring careful risk-benefit assessment before committing to lifelong anticoagulation, 8
Factor V Leiden heterozygosity alone may not significantly increase risk of recurrent venous thrombosis, with studies showing conflicting results, 9
Testing should be done before initiating anticoagulation or at least 2 weeks after discontinuation to avoid interference with functional assays, 5