Factor V Leiden

Factor V Leiden is an inherited blood clotting disorder that raises your risk of deep vein thrombosis or a pulmonary embolism. A mutation in your F5 gene causes this disorder, which follows an autosomal dominant inheritance pattern. Most people with this disorder never develop a blood clot. But if you do, prompt treatment can manage your condition.


What is 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.


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Symptoms and Causes

What causes factor V Leiden?

A genetic mutation (change) causes factor V Leiden. People with this condition have a factor V Leiden mutation, meaning there’s a change in their coagulation factor V (F5) gene. This gene carries instructions that tell your body how to properly create the factor V protein.

Researchers have found that the factor V Leiden mutation involves one small change in the protein’s structure. This change causes factor V to resist the actions of other proteins (protein C and protein S), which normally inactivate factor V when needed to keep your blood from clotting abnormally. As a result, factor V works in overdrive, making your blood more likely to clot when it shouldn’t.

You inherit this condition from one of your biological parents. Factor V Leiden follows an autosomal dominant inheritance pattern. That means only one of your parents has to pass the genetic mutation on to you in order for you to inherit it.

What are the risk factors?

You’re at risk for having factor V Leiden if one of your parents carries a copy of the mutated F5 gene.

If you have the disorder, you may never develop a blood clot. But some factors raise your risk of developing clots. These include:

  • Having additional genetic blood clotting disorders.
  • Undergoing surgery.
  • Being pregnant.
  • Taking estrogen-based therapies.

Talk to your healthcare provider about your risk of developing blood clots and what precautions you should take.

What are the symptoms of factor V Leiden?

The factor V Leiden mutation itself doesn’t cause any symptoms. Most people who inherit it never develop abnormal blood clots, and may never even know they have the disorder. You can have a family history of deep vein thrombosis (DVT) or pulmonary embolism (PE) but never develop either yourself.

However, some people with this disorder develop DVT or PE. It’s important to learn the symptoms so you can seek immediate medical care.

Symptoms of deep vein thrombosis include:

  • Swelling in your leg or arm, which may appear suddenly. Your skin may also feel warm to the touch or look red or discolored.
  • Tenderness or pain in your leg or arm, which you may only feel when standing or moving around.
  • Larger than normal veins near your skin’s surface.
  • Pain in your belly or flank (if blood clots affect veins in your belly).
  • Severe, sudden headache and/or seizures (if blood clots affect veins in your brain).

Symptoms of a pulmonary embolism include:

If you have symptoms of DVT or a PE, call 911 or your local emergency number. Or ask someone to drive you to the nearest emergency room.

What are the complications of factor V Leiden?

Factor V Leiden may lead to deep vein thrombosis or a pulmonary embolism, which are serious medical emergencies. However, most people with this genetic mutation never develop these complications.

Some research shows that factor V Leiden impacts pregnancy. This disorder may raise your risk of a miscarriage or other complications. But there’s no clear consensus, and researchers continue to explore what risks, if any, factor V Leiden poses during pregnancy.


Diagnosis and Tests

How is factor V Leiden diagnosed?

Laboratory testing (blood tests) diagnose this disorder. Your healthcare provider may suspect you have factor V Leiden if you have a history of venous thromboembolism. They may also suspect it if one or more of your biological family members have a history of blood clots.

If your provider feels it’s warranted, they’ll order blood tests, including:

  • Activated protein C (APC) blood test: This coagulation factor screening test checks if your blood has resistance to activated protein C. This is a protein that prevents factor V from going into overdrive. About 9 in 10 people whose blood is resistant to protein C have the factor V Leiden mutation.
  • Genetic testing: If your blood is resistant to protein C, your provider will order genetic testing to check your F5 gene for the factor V Leiden mutation. In some cases, providers order this test without first ordering an APC blood test.

Simply having a family history of blood clots may not be reason enough to run these tests. Your provider will advise you on whether you need testing, as well as on the pros and cons of testing.

Management and Treatment

How is factor V Leiden (FVL) treated?

The factor V Leiden mutation itself doesn’t have any specific treatment. But when a person is diagnosed with an acute deep vein thrombosis (DVT) or pulmonary embolism (PE), treatment with anticoagulants (blood thinners) will be necessary and should be started as soon as possible. Depending on the severity of symptoms, other treatments may be necessary as well. Often, those treatments will require hospitalization.

Individuals who happen to know that they have factor V Leiden — but have never had blood clots — don’t have to be prescribed any blood thinners. But it’s important that these individuals discuss with their doctors what they should be aware of — and what they can do to minimize — the risk of DVT or PE. Some issues that can be discussed with your doctor include:

  • Effective measures to eliminate or reduce other risk factors for DVT or PE, such as smoking cessation, weight loss and having a more active lifestyle.
  • The need (or not) to wear graded elastic compression stockings during long-haul flights and long road trips.
  • Avoidance of alcohol-containing beverages during long flights.
  • Counseling prior to taking birth control pills or before becoming pregnant.


What other complications are associated with factor V Leiden (FVL)?

Other than the increased risk of developing DVT or PE, factor V Leiden may increase the risk of miscarriage or other pregnancy complications, such as preeclampsia and eclampsia, placental abruption (when the placenta separates too early from the wall of your uterus), and having a fetus that grows slower than is usual. Miscarriages associated with factor V Leiden are more likely to occur later in pregnancy (after the first trimester).

But because there are many risk factors associated with the development of those pregnancy complications, there’s still debate and uncertainty as to how much the factor V Leiden mutation is a cause or just another contributing factor to those pregnancy complications.


Can factor V Leiden be prevented?

No, you can’t prevent this blood clotting disorder. There currently aren’t any genetic treatments that can stop someone from inheriting a mutated F5 gene.

Outlook / Prognosis

What can I expect if I have factor V Leiden?

Most people who have this disorder never develop blood clots or have pregnancy complications. But you should talk to your provider about what you can expect in your individual situation.

Does factor V Leiden affect life expectancy?

Factor V Leiden doesn’t affect life expectancy in most people. Even if you develop a blood clot, prompt treatment can prevent a fatal outcome. It’s important to talk to your provider about any concerns you have related to life expectancy or future complications.

Living With

What should you avoid with factor V Leiden?

Talk to your healthcare provider to receive advice tailored to your needs. In general, you should avoid:

  • Smoking, vaping and tobacco use.
  • Long periods of sitting.
  • Drinking too much alcohol, or drinking any alcohol on long plane flights.
  • Taking birth control pills or hormone therapy for menopause without first talking to your provider. These therapies raise the risk of blood clots in people who don’t have a blood clotting disorder. They raise your risk even further.

What can I do to prevent blood clots?

You can help lower your risk of blood clots with lifestyle changes, including:

  • Avoid smoking, vaping and tobacco use. Ask your provider for resources to help you quit.
  • Drink enough water so you stay hydrated.
  • Limit alcohol intake, and avoid it during long flights (it can lead to dehydration).
  • Keep a weight that’s healthy for you.
  • Move around more. Try to build up to 150 minutes of moderate-intensity exercise (like walking) per week.
  • Stand up and walk around during long flights. Take frequent breaks during long car rides to get out and stretch your legs. If you can’t walk around, flex your ankles and point your toes up and down.
  • Wear compression stockings if your provider prescribes them for you. Don’t buy ones from the store or wear them without talking to your provider first.

When should I see my healthcare provider?

Visit your provider for a yearly checkup. If you’ve been diagnosed with DVT or a PE, you’ll have frequent follow-up appointments so your provider can check treatment progress. If you’re taking warfarin, you’ll need routine blood testing (prothrombin time test) to check how well your medication is working. It’s important to go to all of your appointments and talk to your provider about any questions or concerns you have.

It’s also important to talk to your provider:

  • Before using birth control pills or hormone therapy for menopause.
  • Before becoming pregnant.

When should I go to the emergency room?

Seek emergency medical care if you develop symptoms of deep vein thrombosis or a pulmonary embolism. These conditions can be life-threatening and require immediate medical treatment. The sooner you receive care, the better your chances of a good outcome.

What questions should I ask my doctor?

If you have factor V Leiden, you may have many questions. Here are a few to help you start the conversation:

  • What can I do to help prevent blood clots from forming?
  • What can I do to support a healthy pregnancy?
  • What are the chances of passing down the genetic mutation to my children?
  • Do you recommend genetic testing for any of my family members?

Additional Common Questions

What is the difference between factor V and factor V Leiden?

Factor V is a coagulation factor, or protein, in your blood. Factor V and other proteins work together to help your blood clot when necessary. These proteins are essential helpers that support hemostasis. This is your body’s reaction to an injury that prevents you from bleeding too much. But if you have a blood clotting disorder, your blood forms clots more easily than normal.

Factor V Leiden is the name of one such blood clotting disorder. This disorder affects factor V, as opposed to other proteins in your blood. “Leiden” is the city in the Netherlands where researchers discovered the condition.

A note from Cleveland Clinic

If you or a loved one have factor V Leiden, you might feel scared about what the future will bring. Maybe you’ve already had to deal with a blood clot and wonder if you’ll face another. Or maybe you’ve had no issues, but your loved one needed treatment for DVT. You’re might be wondering, “Will this happen to me? What are my risks? What about my children?”

The questions may keep coming, and that’s normal. As they come, write them down. Take your questions to your healthcare provider and get the answers you need. It may ease your mind to know that most people with this disorder never have a blood clot. But if you do develop clots, be assured there are treatments that can help. Following your provider’s guidance can help you catch and resolve problems early before they interrupt the flow of your life.

Medically Reviewed

Last reviewed on 10/04/2022.

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