Factor V Leiden

Factor V Leiden (pronounced “FAK-ter five LYE-den”) is a blood clotting disorder that raises your risk of abnormal blood clots. It’s the most common blood clotting disorder that’s inherited, or passed down within biological families.

People with factor V Leiden have a mutation in their coagulation factor V (F5) gene. Your F5 gene controls the production of a protein called factor V, which helps your blood clot when needed (such as after an injury). The factor V Leiden mutation changes this protein’s structure. This change causes it to resist other proteins that stop excessive clotting. As a result, your blood may clot more easily than it should, leading to serious complications.

How does factor V Leiden affect my body?

Factor V Leiden makes you more likely to develop:

• Deep vein thrombosis (DVT): This is the formation of blood clots in the deep veins of your legs or arms. Rarely, blood clots can form in the veins of your liver, kidneys, brain or intestines. Factor V Leiden has a strong association with DVT. Up to 1 in 5 people who develop DVT for the first time have Factor V Leiden.
• Pulmonary embolism (PE): This is a blood clot that travels through your bloodstream to one of your lungs. Factor V Leiden isn’t as strongly associated with PE as with DVT, but it still raises your risk.

It’s important to know that people with factor V Leiden won’t necessarily develop DVT or PE. In fact, the vast majority (9 out of 10) never develop abnormal blood clots. However, the disorder raises your risk compared to people without the disorder.

If you have this disorder, you may experience:

• DVT or a PE before age 50.
• Multiple episodes of DVT or PE.
• Blood clots in less commonly affected veins, like those in your liver or brain.
• DVT or a PE during or shortly following pregnancy.
• DVT or a PE soon after starting birth control pills or hormone therapy.

Factor V Leiden doesn’t raise your risk of heart attacks, strokes or blood clots in the arteries of your legs.

How common is this condition?

The prevalence of factor V Leiden varies by ethnicity. In general, it’s more common among people who are white in the U.S. and Europe.

In the U.S., this disorder affects:

• About 1 in 20 people who are white.
• Up to 1 in 50 people who are Black, Hispanic or Native American.
• Fewer than 1 in 100 people of Asian descent.