Factor V Leiden Mutation

The factor V Leiden mutation is a single‑nucleotide change in the F5 gene (Arg506Gln) that makes factor V resistant to inactivation by activated protein C. This activated protein C resistance leads to prolonged clotting activity and substantially increases risk of venous thromboembolism—heterozygotes have moderately elevated risk, while homozygotes face a much higher risk of DVT and pulmonary embolism.

Factor V Leiden is the most common inherited clotting mutation and raises risk of venous thromboembolism. Heterozygotes have about a 3–8× higher risk; homozygotes carry substantially greater risk. Many carriers never develop clots, but risk increases with pregnancy, surgery, oral contraceptives, or other prothrombotic conditions. Severity ranges from low for isolated heterozygosity to high when homozygous or combined with other risks; treatment may include anticoagulation.

Factor V mutations (including Factor V Leiden) are inherited in an autosomal manner, so they can be passed on by either the mother or the father. If one parent carries the mutation, each child has about a 50% chance of inheriting it. If both parents carry it, a child can inherit two copies (homozygous), which substantially raises clotting risk.

Avoid things that increase clot risk: estrogen-containing birth control or hormone-replacement therapy, smoking, prolonged immobility (long flights or bed rest) without movement, dehydration, and untreated obesity. Also review medications (for example tamoxifen) and planned surgery or pregnancy with your doctor so you can get appropriate clot-prevention measures. Carry medical ID and follow specialist advice.

Yes — often you can donate blood with factor V Leiden if you’ve never had a clot and aren’t taking anticoagulants. If you’ve had venous thromboembolism, are homozygous, or are on warfarin/DOACs, you’ll usually be deferred. Always declare the condition during donor screening and check with your national blood service or clinician for individual guidance.

The V factor is also known as Factor V, proaccelerin or the labile factor. It’s a clotting protein made by the liver and platelets that functions as a cofactor in the prothrombinase complex, speeding conversion of prothrombin to thrombin. Genetic variants—most notably Factor V Leiden—can make it resistant to degradation, raising the risk of abnormal blood clots.