Laboratory Screening for Multiple DVTs Including Factor V Leiden
For a patient with recurrent (multiple) deep vein thromboses, you should perform comprehensive thrombophilia testing including Factor V Leiden, prothrombin G20210A mutation, functional assays for antithrombin III, protein C, and protein S, plasma homocysteine levels, and testing for antiphospholipid antibodies (lupus anticoagulant and anticardiolipin antibodies). 1
Recommended Testing Panel
The presence of multiple DVTs is a clear indication for thrombophilia screening, as recurrent venous thrombosis is one of the strongest indications for testing regardless of age 1. Here's the specific workup:
Primary Genetic Testing
- Factor V Leiden (R506Q mutation): Use direct DNA-based genotyping as the preferred method 1. This is particularly important as it's present in 90-95% of cases with activated protein C resistance 2.
- **Prothrombin G20210A mutation (Factor II c.*97G>A)**: Should be tested simultaneously with Factor V Leiden, as the DNA test is equally simple and can be multiplexed 1
Functional Coagulation Assays
- Antithrombin III deficiency: Functional assay
- Protein C deficiency: Functional assay
- Protein S deficiency: Functional assay
These functional assays are essential because these deficiencies are too genetically heterogeneous for routine molecular testing but are important risk factors, especially with a strong family history 1
Additional Testing
- Plasma homocysteine levels: This is preferred over MTHFR genetic testing, as homocysteine measurement is more informative and hyperhomocysteinemia interacts synergistically with Factor V Leiden to increase VTE risk 20-fold 1
- Lupus anticoagulant and anticardiolipin antibodies: To evaluate for acquired thrombophilias 1
Key Clinical Considerations
Why This Comprehensive Approach?
Venous thrombosis is multifactorial, and multiple genetic risk factors commonly coexist 1. Approximately 50% of first-time VTE cases are unprovoked, and known genetic factors are present in about 25% of the screening population without family history and up to 63% of familial cases 2. Recurrent thrombosis carries significant morbidity and mortality, making risk stratification through panel testing crucial for targeting anticoagulation therapy to those at highest risk 1.
Testing Methodology
For Factor V Leiden specifically, either direct DNA-based genotyping or a Factor V Leiden-specific functional assay is acceptable 1. However, if using a functional assay initially and it's positive, confirm with DNA testing to distinguish heterozygotes from homozygotes, as this affects risk stratification 1.
Important Pitfalls to Avoid
- Timing of testing: Ideally perform testing when the patient is not on anticoagulation, as heparin and warfarin can interfere with functional assays for protein C, protein S, and antithrombin III
- Don't stop at Factor V Leiden alone: The guidelines explicitly recommend testing for other thrombophilias when Factor V Leiden testing is indicated 1
- Age is not a limiting factor: While some physicians exclude testing in patients over 60, studies show that among Factor V Leiden carriers, the first lifetime episode often occurs after age 50 1
Clinical Utility
The identification of specific thrombophilias in patients with recurrent DVT directly impacts management decisions regarding duration of anticoagulation therapy and prophylaxis in high-risk situations 3. The presence of multiple risk factors significantly increases recurrence risk and may justify extended or lifelong anticoagulation 1.