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Factor V (Leiden) Mutation Analysis

Test code(s) 22722, 36192 (NY), 17900X, 17901X (NY)

Question 1. What does it mean if my patient is heterozygous for factor V Leiden?

This test detects the presence or absence of only one mutation in the factor V gene. This mutation is known as factor V Leiden, R506Q, or G1691A. An individual who is heterozygous has one copy of the factor V gene that carries the Leiden mutation and one copy that does not carry the mutation. Individuals who are heterozygous carriers of the mutation have an increased risk for thromboembolism. This increased risk is not as high as that conferred by 2 copies (homozygous) of the factor V Leiden mutation.

The coagulation pathway is complex, and it is important to interpret the factor V Leiden results in the context of other genetic results, environmental exposures (such as smoking), personal history of thrombosis, and family history of thrombosis.1

Question 2. My patient told me that their relative was positive for a factor V mutation. How do I interpret my patient’s result in the context of this family history?

While the Leiden mutation is the most common mutation tested for in the factor V gene, the gene is large, and many different mutations affecting its function have been described. It is important to confirm that your patient’s relative did have genetic testing for factor V Leiden and that factor V Leiden is the cause of the relative’s thrombophilia before you can interpret your patient’s result. 

If you have confirmed that the relative is indeed heterozygous or homozygous for factor V Leiden and your patient is negative for this mutation, your patient’s risk of thrombosis is reduced to that of the general population provided that all other thrombosis risk factors have been taken into consideration.     

Question 3. Are the factor V Leiden results affected by the fact that my patient is taking a medication such as a blood-thinner?

No, genetic (mutation) testing is not affected by medications.     

Reference

  1. Varga E. Inherited thrombophilia: key points for genetic counseling. J Genet Couns. 2007;16(3):261-277.
This FAQ is provided for informational purposes only and is not intended as medical advice. A physician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.
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