Factor V Leiden: Blood Clotting Disorder

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 Leiden, also called FVL, is a change in your genes (the doctor will call it a mutation) that keeps this process from working right. It's leads to a condition called factor V Leiden thrombophilia.

It works like this: 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 causes hypercoagulability, which makes it harder for your clots to break up. If the clots don't go away, you're more likely to have one in the veins in your legs. This is called deep venous thrombosis (DVT). You're also at higher risk for having clots that travel through your bloodstream. These can cause a blockage in the arteries in your lungs, known as pulmonary embolism (PE).

You get it from your genes. That means you were born with a gene mutation that causes it. You can get it from one or both of your parents.


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

The signs of a clot include:

  • Pain
  • Redness
  • Swelling
  • Warmth

A deep vein clot (DVT) typically shows up in your leg. It 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:


Your doctor will ask about your medical history and any clots you or any family members may have had.


Your doctor probably will want to take a sample of your blood for some tests:

Activated protein C resistance test: Protein C blocks other proteins from forming clots. If you don’t have enough or it isn’t doing what it should, your blood may clot too much.

Dilute Russell viper venom time or lupus anticoagulant test: This test looks for lupus anticoagulants, which are proteins that can throw off the clotting process. Clotting time for your blood plasma in a solution of venom from this deadly Indian snake is compared to that of a control plasma.

Genetic test: If the blood test results aren't clear, your doctor might recommend a genetic test to help confirm your diagnosis. This is typically done with a sample of your blood. It can tell you if you have the factor V problem gene and if you got it from one or both parents.

Who's at Risk?

If you inherited the factor V problem gene from both your parents, you're more likely to develop it. If you have only one copy of the gene, your chances are lower.

You're more likely to have the problem gene if you're white and of European descent. In the U.S., about 5% of white people have it.

The kinds of birth control that use hormones -- such as the pill, ring, or patch -- may increase your odds of getting a DVT or PE. So does hormone replacement therapy. But if you use these and have factor V Leiden, your risk of getting these clots is 15 to 35 times higher than normal.

Pregnant women with factor V Leiden are more likely to get a DVT than women who don't have the disorder. Most women with factor V Leiden don't have any issues, but be sure to tell your doctor if you have it, especially if you've had blood clots in the past.

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

  • You had a DVT or PE before turning 50.
  • You have a DVT or PE that keeps coming back.
  • You have a clot in your brain or liver.
  • You had a DVT or PE during or right after a pregnancy.
  • You have a history of miscarriages in the second or third trimester.
  • You have a strong family history of venous thromboembolism and you have a DVT or PE.



Factor V Leiden can't be cured because it's a problem with a gene. But if you have it and have a blood clot, your doctor can prescribe blood thinners (he might call them anticoagulants), Two of the most common are:

Heparin. This medication works quickly. Your doctor can inject it into a vein (intravenously) or under the skin (subcutaneously). Or you may able to give yourself the injection. This drug is safe for pregnant women.

Caution: Possible risks of heparin include excess bleeding and allergic reaction. There’s no standard dose, so you’ll need to see your doctor to get blood tests that will help them figure out how much is right for you. You may need adjust the dose from time to time, too.

Warfarin (Coumadin, Jantoven). You’ll take this medication as a pill. There’s no standard dose for it, either, so as with heparin, you'll need see the doctor often for tests and adjustments while taking warfarin.Caution: It can cause bleeding, and it isn’t safe for pregnant women, especially the first trimester. Tell your doctor about anything 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 require testing and adjustments, but might make you more likely to bleed. These include:

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

You probably won't take any of these medications for life if you've only had one DVT or PE unless you also have other things that make these conditions more likely.


Lifestyle Changes

If you don’t have a blood clot, your doctor will probably skip medication and tell you to do things to help prevent one. These include:

  • See your doctor often. She’ll let you know if your medications are helping and make adjustments if you need them. If you're taking warfarin, you'll get a blood test to see how well your blood is clotting.
  • Make sure you aren’t bleeding too much. This is a side effect of blood thinner medications. Even a small cut can get serious when you're taking blood thinners.
  • Be safe: Talk to your doctor about things that can lead to bruises or cuts. Try not to bump or injure your legs. Don’t cross your legs.
  • 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 more 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.
  • Wear compression stockings. They aren’t pretty, but they’ll help keep you from getting another 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 it and your cholesterol levels low can help you avoid another blood clot.
  • Quit smoking. It affects blood flow and circulation, which can raise your risk of another 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 can also 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 it 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 (your doctor may call this pre-eclampsia) or early separation of the placenta from the uterine wall (also 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 its original site, travels through your bloodstream and lands in your lungs. It can stop your heart from pumping and taking in oxygen.

WebMD Medical Reference Reviewed by Nayana Ambardekar, MD on July 15, 2018



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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."

NIH U.S. 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.”

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