Factor V Leiden

What Is Factor V Leiden?

Factor V Leiden (FVL) is a change in your genes that keeps your body’s blood-clotting process from working right. It can cause a disorder called factor V Leiden thrombophilia.

When you get a cut or scrape, your body forms a clot to stop the bleeding. Clots are clumps of blood cells called platelets and the liquid part of your blood called plasma. Factor V (factor 5) is one of several special proteins in your blood that help it clot. They’re called clotting factors. Once the bleeding stops, other proteins tell your clotting factors to break up the clot, and it goes away.

Factor V Leiden makes it harder for your clots to break up. If the clots don't go away, you're more likely to have them in the veins in your legs. This is called deep vein thrombosis (DVT). You also have higher chances of getting clots that travel through your bloodstream. These can block the arteries in your lungs, which is called pulmonary embolism (PE).

Factor V Leiden is also known as Leiden type, APC resistance, and hereditary resistance to activated protein C.

Factor V Leiden Symptoms

Some people who have factor V Leiden may never know. When there are signs, the first is usually a clot somewhere in your body. The clots can be minor or life-threatening, depending on where they are.

The signs of a clot include:

  • Pain
  • Redness
  • Swelling
  • Warmth

DVT causes the same symptoms but with more swelling.

Pulmonary embolisms caused by traveling clots can damage your lungs and can even be fatal. Symptoms include:

Factor V Leiden Causes and Risk Factors

You get factor V Leiden because of your genes. That means you were born with a change or “mutation” that causes it. You can get it from one or both of your parents.

About 5% of people in the United States have factor V Leiden. It’s most common in people of Northern European descent.

If you've had any of these signs, get checked for factor V Leiden:

  • DVT or PE before turning 50
  • DVT or PE that keeps coming back
  • A clot in your brain or liver
  • DVT or PE during or right after a pregnancy
  • Pregnancy loss in the second or third trimester
  • A strong family history of venous thromboembolism and a personal history of DVT or PE


Blood Clot Risk Factors

Some things can make anyone more likely to get a blood clot:

  • Older age
  • Obesity
  • Smoking
  • Birth control with hormones -- such as the pill, ring, or patch -- or hormone replacement therapy
  • Pregnancy
  • Sitting still for a long time, like on a plane
  • Surgery or injury, such as a broken bone
  • A blood type other than type O

Clots are also more likely in people who have factor V Leiden and another change in the F5 gene, or FVL along with changes in another gene involved in blood clotting.

Factor V Leiden Treatment

There’s no cure for factor V Leiden. If you have a blood clot, if you’re pregnant, or if you need to have surgery, your doctor can prescribe blood thinners (called anticoagulants). Two of the most common are:

  • Heparin. This medication works quickly. Your doctor can inject it into a vein (intravenously) or under your skin (subcutaneously). Or you may able to give yourself the injection. This drug is safe for pregnant women. Heparin may have side effects including excess bleeding and allergic reaction. There’s no standard dose, so you’ll need to have blood tests that will help your doctor figure out how much is right for you. You may need to adjust the dose from time to time, too.
  • Warfarin (Coumadin, Jantoven). You take this medication as a pill. There’s no standard dose for it, either, so as with heparin, you'll need to see the doctor often for tests and adjustments.  It can cause bleeding, and it isn’t safe for pregnant women, especially the first trimester. Tell your doctor about anything else you’re taking when you start warfarin. It can affect the way other drugs and herbs work.

Or you might take anticoagulant pills that don’t need testing and adjustments but might make you more likely to bleed. These include:

  • Apixaban (Eliquis)
  • Dabigatran (Pradaxa)
  • Rivaroxaban (Xarelto)

Lifestyle changes

If you don’t have a blood clot, your doctor will talk to you about ways to prevent one. These include:

  • Be safe. Avoid bruises and cuts. Try not to bump or injure your legs. Don’t cross your legs when you sit down. Choose solo exercise rather than contact sports. At home, use a soft toothbrush and an electric razor. Be careful with knives, scissors, and other household tools.
  • Stay active. Even if you've been on bed rest after surgery or for other reasons, get moving as soon as your doctor gives you the OK. That’s a sure way to help prevent blood clots. Don’t sit or stand still for more than an hour at a time. Change positions often, especially if you’re on a long trip.
  • Be smart about hormones. Talk to your doctor before getting pregnant or starting hormone replacement therapy.
  • Wear compression stockings. They aren’t pretty, but they’ll help keep you from getting a clot.
  • Eat a healthy, low-salt diet. Extra pounds put more pressure on the veins in your pelvis and legs. Salt boosts your blood pressure. Keeping sodium and cholesterol low can help you avoid a blood clot.
  • Quit smoking. It affects blood flow and circulation, which can raise your risk of a clot.​​​​​​​
  • Lift up. Raise the bottom of your bed 6 inches off the ground. You can use blocks, books, or special risers you can find online or at home stores.


Factor V Leiden Complications

Factor V Leiden can raise your chances of other problems and conditions.

Deep vein thrombosis. This is when your blood thickens and forms a clot in a vein. These can happen anywhere in your body, but they most often affect one leg. They’re especially likely if you’ve been sitting for hours at a time, like when you’re on a long flight.

Pregnancy issues. Women who have factor V Leiden are two to three times more likely to lose a baby in the second or third trimester. This can happen more than once. It can also make you more likely to get high blood pressure during pregnancy (called preeclampsia) or early separation of the placenta from your uterine wall (called placental abruption). Factor V Leiden can also make your baby grow more slowly.

Pulmonary embolism. This is when a blood clot breaks away from where it formed, travels through your bloodstream, and lands in your lungs. It can stop your heart from pumping and taking in oxygen.

Factor V Leiden Outlook

Most people who have factor V Leiden never get blood clots, and most women have healthy pregnancies.

If your doctor prescribes medication, you probably won’t need to take it for life if you've had only one DVT or PE, unless you also have other things that make these conditions more likely.

WebMD Medical Reference Reviewed by Gabriela Pichardo on May 10, 2020



American Society of Hematology: "Blood Clots."

CDC: "Venous Thromboembolism (Blood Clots)."

GeneFacts: "Factor V Leiden-associated Thrombosis."

Mayo Clinic: "Factor V Leiden."

National Blood Clot Alliance: "Factor V Leiden Resources."

National Human Genome Research Institute: "Learning About Factor V Leiden Thrombophilia."

National Library of Medicine Genetics Home Reference: "factor V Leiden thrombophilia."

World Federation of Hemophilia: "What are rare clotting factor deficiencies?"

Lab Tests Online: “Protein C and Protein S.”

Society for Vascular Surgery: “Deep Vein Thrombosis,” “Pulmonary Embolism.”

Journal of Thrombosis and Haemostatis: “A two‐step coagulation test to identify antiβ2‐glycoprotein I lupus anticoagulants.”

University of Michigan: “Russell’s Viper.”

Mayo Clinic: “Deep vein thrombosis."

Medscape: “Factor V Leiden and Contraception.”

National Center for Advancing Translational Sciences Genetic and Rare Diseases Information Center: “Factor V Leiden thrombophilia.”

Cleveland Clinic: “Factor V Leiden.”

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