From the Guidelines
Screening for factor V Leiden mutation is typically done through genetic testing of a blood sample, using a DNA-based test called polymerase chain reaction (PCR), which specifically identifies the genetic mutation responsible for factor V Leiden, as recommended by the American College of Medical Genetics consensus statement 1. The primary method of screening is a DNA-based test, which can determine if a person is heterozygous (one copy of the mutation) or homozygous (two copies), affecting the degree of thrombosis risk. Before genetic testing, doctors may first perform a functional screening test called activated protein C resistance (APCR) assay, which measures how well a patient's blood responds to activated protein C, as noted in the study by 1. An abnormal APCR result suggests factor V Leiden but requires confirmation with the DNA test. Testing is typically recommended for individuals with:
- Unexplained venous thromboembolism (especially at a young age)
- A strong family history of blood clots
- Thrombosis in unusual locations
- Recurrent pregnancy loss The test requires a standard blood draw and results are usually available within a few days to weeks. No special preparation is needed before the test, though patients should inform their healthcare provider about any blood-thinning medications they're taking, as these won't affect genetic test results but are relevant to overall care, as stated in the guidelines by 1. It's also important to consider the patient's age, with testing recommended for those under 50 with any venous thrombosis, and for those with a strong family history of thrombotic disease, as recommended by 1. Additionally, testing may be considered for women with recurrent pregnancy loss or unexplained severe preeclampsia, placental abruption, intrauterine fetal growth retardation, or stillbirth, as noted in the study by 1. Random screening of the general population for factor V Leiden is not recommended, as stated in the guidelines by 1. Overall, the decision to screen for factor V Leiden mutation should be based on individual patient risk factors and medical history, as recommended by the American College of Medical Genetics consensus statement 1.
From the Research
Screening Methods for Factor V Leiden
To screen for Factor V Leiden mutation, several methods can be employed, including:
- Activated Protein C resistance assay, a coagulation screening test 2
- DNA analysis of the F5 gene, which encodes the Factor V protein 2
- Russell viper venom time-based assay, which can be performed on whole blood or platelet-poor plasma 3
- Polymerase chain reaction (PCR) for the FV Leiden defect, followed by detection with lanthanide-labeled probes 4
- Modified activated partial thromboplastin time (APTT) using FV-deficient plasma 3
Recommendations for Screening
The decision to screen for Factor V Leiden should be made on an individual basis, taking into account the patient's family history and personal risk factors for thrombosis 5, 2.
- Patients with a family history of thrombosis may be at increased risk of carrying the Factor V Leiden mutation, but a family history is not a reliable criterion for detecting carriers 5
- Screening may be worthwhile even if the advantages of oral contraception are higher than the thrombotic risk 5
- Asymptomatic Factor V Leiden heterozygotes do not require long-term anticoagulation, but prophylactic anticoagulation may be considered in high-risk clinical settings 2
Laboratory Testing Methods
The preferred laboratory testing methods for Factor V Leiden include: