Factor II and Factor V (Leiden) Genotyping
Factor V and II are blood clotting proteins. Variations in these proteins may increase the risk of dangerous cardiovascular events caused by venous thrombosis. In clinical studies, it has been shown that several genetic defects are associated with increased risk of venous thrombosis. Physicians should consider testing any patient who has had a personal or family history of such events or those at high clinical risk of venous thrombosis, including patients taking medications that are potential contributors. Genetic variants tested are Factor II: c.*97G>A (g.20210G>A) and Factor V Leiden: c.1601G>A (c.1691G>A).
Indications for Factor II and Factor V Mutation Testing
Individuals with a personal or family history of first or recurrent venous thrombosis; who have had venous thrombosis at a young age (less than 50), venous thrombosis in unusual sites (hepatic, mesenteric, cerebral veins) or venous thrombosis in pregnancy; or with a combination of those who are also taking medications which individually increase the risk for venous thrombosis.
CPT Codes: 81241 and 81240 (provided for your guidance only).
Please call Client Services at 800-837-8362 to order testing supplies.
- Buccal Swabs: 4 sterile buccal swabs (preferred)
- Blood: 5-10cc whole blood lavender-top EDTA or yellow-top ACD-A tubes
- Turnaround Time: 10 business days, faster turnaround available for clinical trials
Variants to Factor V and Factor II may affect a patient’s risk of blood clotting problems. The Factor V variant known as Factor V Leiden (or rs6025) is associated with an approximately 300% increased risk in heterozygotes and an up to 8000% increased risk in homozygotes. The Factor II rs1799963 polymorphism (or G20210A) may also independently increase the risk by approximately 200%. 
Factor V testing is clinically actionable and recommended by the American College of Medical Genetics with Factor II as a tandem test. Patients should be counseled about the implications of their results by their physician or genetic counselor.
Certain polymorphisms show differing prevalence based on ethnic background.
Frequency of Factor II and Factor V Alleles with Clinical Relevance
|Gene||Allele||Enzyme Activity||Caucasian||African||Hispanic||Native American||Asian|
|Factor V||Leiden (rs6025)||Decreased||2 – 5%||1.23%||2.21%||0.45%||1.25%|