From the Guidelines
Factor V Leiden (FVL) testing should involve a combination of activated protein C resistance (APCR) as an initial screening test, followed by genetic testing for the specific Factor V Leiden mutation if APCR is abnormal, as recommended by the American College of Medical Genetics consensus statement 1. The recommended labs for FVL testing include:
- Activated protein C resistance (APCR) as an initial screening test
- Genetic testing for the specific Factor V Leiden mutation if APCR is abnormal
- Prothrombin G20210A mutation
- Protein C and protein S levels
- Antithrombin III activity
- Lupus anticoagulant
- Anticardiolipin antibodies
- Beta-2 glycoprotein antibodies
- Complete blood count
- Basic coagulation studies (PT/INR, PTT)
- Homocysteine levels These tests should be performed when the patient is not on anticoagulation therapy if possible, as medications like warfarin and heparin can affect results, as noted in the American College of Medical Genetics consensus statement 1. Testing is most appropriate for patients with:
- Unprovoked venous thromboembolism
- Thrombosis at unusual sites
- Recurrent thrombotic events
- A strong family history of thrombosis The genetic basis of FVL involves a point mutation that makes Factor V resistant to degradation by activated protein C, resulting in a hypercoagulable state and increased thrombosis risk, as discussed in the American College of Medical Genetics consensus statement 1. Additionally, testing may also be considered in certain situations, such as:
- Venous thrombosis, age >50, except when active malignancy is present
- Relatives of individuals known to have factor V Leiden
- Women with recurrent pregnancy loss or unexplained severe preeclampsia, placental abruption, intrauterine fetal growth retardation, or stillbirth, as recommended by the American College of Medical Genetics consensus statement 1.
From the Research
FVL Checking Labs
- Factor V Leiden (FVL) is an inherited condition that predisposes individuals to thrombosis, and it can be detected through laboratory tests 2.
- The tests for FVL include screening for activated protein C (APC) resistance, and if positive, testing for the Factor V Leiden mutation 2.
- FVL mutation is the most common known hereditary defect predisposing to venous thrombosis, and its diagnosis is highly accurate 3.
- Laboratory biomarkers, such as high familial penetrance and distinctive aspects of the first thrombotic event, can guide the optimal management of secondary antithrombotic prophylaxis, primary prophylaxis in asymptomatic individuals, and whether to screen relatives 3.
- The management guidelines for affected patients are quickly evolving but are still limited by a lack of clinical data 4.
- Long-term, low-dose warfarin has been studied as a potential treatment for patients with venous thrombosis and FVL mutation, but its efficacy and safety are still being researched 5.
- Direct oral anticoagulants (DOACs) have been compared to warfarin in patients with high-risk hereditary thrombophilia, including FVL, and have shown promising results in terms of efficacy and safety 6.
Laboratory Testing for FVL
- Screening for APC resistance is the initial step in detecting FVL 2.
- If the screening test is positive, further testing for the FVL mutation is necessary to confirm the diagnosis 2.
- Laboratory tests for FVL are crucial in identifying individuals with this inherited condition and guiding their management and treatment 3.
- The choice of anticoagulant therapy, such as warfarin or DOACs, depends on various factors, including the patient's risk of thrombosis and bleeding, and laboratory test results 5, 6.
Clinical Relevance of FVL Checking Labs
- FVL checking labs play a critical role in the diagnosis and management of patients with venous thrombosis and inherited thrombophilia 3.
- The results of laboratory tests for FVL can inform clinical decisions regarding anticoagulant therapy, thromboprophylaxis, and family screening 3, 4.
- Further research is needed to optimize anticoagulant management in patients with high-risk hereditary thrombophilia, including FVL 6.