Factor V Leiden

Date Updated: 05/12/2026

Overview

Factor V Leiden (FAK-tur five LIDE-n) is a change of one of the clotting factors in the blood. A clotting factor is a protein that helps blood to clot. This change can raise the risk of getting harmful blood clots, most often in the legs or lungs.

Most people with factor V Leiden never get harmful clots. But people who do get them need to take blood thinners. Blood clots can lead to long-term health issues. And they can be life-threatening.

People assigned male at birth or female at birth can have factor V Leiden. People who carry the changed gene in factor V Leiden may be more likely to get blood clots during pregnancy or when taking the hormone estrogen.

There is treatment for people who have factor V Leiden and get blood clots. Anticoagulant medicines, also called blood thinners, can lower the risk of getting more blood clots and having serious complications.

Symptoms

Having changed gene that causes factor V Leiden itself doesn't cause symptoms. Getting a blood clot in the legs or lungs may be the first sign of having the condition.

Some clots do no damage and go away on their own. Others can be life-threatening. Symptoms of a blood clot depend on what part of the body it affects.

A clot in a deep vein

This is known as deep vein thrombosis, also called DVT. This most often happens in the legs. A clot in a deep vein may not cause symptoms. If there are symptoms, they may include:

Pain.
Swelling.
Redness. This may be harder to see on Black skin or brown skin.
Warmth.

A clot that travels to the lungs

This is called a pulmonary embolism. It happens when part of a clot in a deep vein breaks free and travels through the right side of the heart to the lung. In the lung, it blocks blood flow. This can be life-threatening.

Symptoms may include:

Sudden shortness of breath.
Chest pain when breathing in.
A cough that makes bloody or blood-streaked mucus.
Rapid heartbeat.

When to see a doctor

Seek medical help right away if you have symptoms of either a deep vein thrombosis or a pulmonary embolism.

Causes

People who have factor V Leiden get either one copy or, rarely, two copies of the changed gene from their parents. Having one copy of the changed gene slightly raises the risk of getting blood clots. Getting two copies, one from each parent, greatly raises the risk of getting blood clots.

Risk factors

A family history of factor V Leiden raises the risk of getting the condition. The condition is most common in people who are white and whose families are from Eastern Europe.

People who get the factor V Leiden gene change from only one parent have a 5% chance of getting a blood clot by age 65. Factors that raise this risk include:

Two changed genes. Getting the changed genes from both parents instead of just one can greatly raise the risk of blood clots.
Not moving.. Long periods of not moving, such as sitting during a long airplane flight, can raise the risk of leg clots.
The hormone estrogens. Birth control pills, hormone replacement therapy and pregnancy can raise the risk of getting blood clots.
Surgeries or injuries. Surgeries or injuries such as broken bones can raise the risk of blood clots.
Certain blood types. People who have blood types A, B or AB have a higher risk of blood clots than those with blood type O.

Complications

Factor V Leiden can cause blood clots in the legs, called deep vein thrombosis, and lungs, called pulmonary embolism. These blood clots can be life-threatening.

Diagnosis

A blood test can confirm the diagnosis of factor V Leiden. The test may be a blood-clotting study or a genetic test. Your healthcare professional may order the test if you've had one or more blood clots or if you have a strong family history of blood clots.

Treatment

Healthcare professionals most often prescribe blood-thinning medicines to treat people who get blood clots. People who have the factor V Leiden gene change but who have not had blood clots don't need this medicine.

If you have the factor V Leiden gene change and you need to have any type of surgery, your healthcare professional might suggest that you take extra care to prevent blood clots. This may include:

Taking blood thinners for a short time.
Using leg wraps that inflate and deflate to keep blood moving in your legs.
Wearing stockings that put pressure on your legs, called compression stockings.
Going for walks soon after surgery.

For people who are pregnant and have the factor V Leiden gene, a healthcare professional may suggest taking blood thinners during pregnancy and for a time after giving birth.

Lifestyle and home remedies

Some ways to help lower your risk of blood clots include:

Keep your legs moving. When you move your legs, the muscles tighten. This tightening, called contracting, helps blood move through your body.

On a long plane trip, raise your toes up and down, and rotate your ankles every hour or so. Drink extra water to keep from losing fluids. Don't drink alcohol. On a car trip, take breaks every so often and walk around.
Wear compression stockings.These stockings most often come up to the knees. They help keep blood moving by pressing on your legs. Ask your healthcare professional if they might help you.
Be careful about taking the hormone estrogen. Birth control pills or estrogen replacement therapy can raise the risk of blood clots. So talk with your healthcare professional before taking medicines with estrogen if you have factor V Leiden.

Prevent bleeding

If you take blood-thinning medicine for factor V Leiden, these steps might help you prevent injury and keep you from bleeding too much:

Don't play contact sports or do other activities that could result in injury. Do regular, gentle exercise for good health. Exercises might include walking or swimming.
Use a soft toothbrush and waxed floss.
To keep from cutting yourself while shaving, use an electric razor.
Be careful with household tasks that involve knives, scissors and other sharp tools.

Preparing for an appointment

Your healthcare professional may send you to a specialist in genetic conditions, called a geneticist, or a specialist in blood conditions, called a hematologist. They can test to see whether changed genes are the cause of your blood clots and whether you have factor V Leiden.

Here's some information to help you get ready for your appointment.

Make a list of:

All your symptoms, and when they began.
Your health history, including your history of blood clots. Include any family history of blood clots or family members that have factor V Leiden.
All medicines, vitamins and supplements you take, including dosages.
Questions to ask your healthcare professional.

For factor V Leiden, some questions to ask your healthcare professional include:

What tests do I need?
Do I need to see a specialist?
Do I need treatment for factor V Leiden? Does that include medicine to prevent blood clots?
What types of side effects can I expect from the medicine?
Do I need to limit my activity?
Do my children need to be tested?
Do you have brochures or other printed material that I can have? What websites do you suggest?

If your healthcare professional suggests genetic testing, some questions to ask the genetic specialist may include:

How likely is this test to be right?
What are the risks of the test?
What will a positive or negative result tell me?
Can the results of the test affect my health insurance?
What would a test result that isn't certain mean?
What are my treatment options if I have factor V Leiden?
Should my children be tested?
How long will it take to get the test results?