Patient education: Factor V Leiden (The Basics)

What is factor V Leiden? — 

Factor V Leiden, or "FVL," is a genetic condition that can increase the risk of blood clots. Most people with the FVL gene do not know that they have it because they don't have any symptoms. But some people with the gene can get blood clots in their legs, lungs, and other parts of their body.

The letter "V" is the Roman numeral for "5," so "factor V" means "factor 5." Leiden is a city in Holland where the condition was discovered.

FVL is a lifelong condition a person is born with. It is caused by a single change in the gene that the body uses to make a protein called factor V. This protein helps the blood clot.

People with FVL can get the changed gene from 1 or both of their parents. Usually, it comes from just 1 parent. People who get 2 copies of the gene (from both parents) have a higher risk of blood clots.

About 4 to 5 percent of White people have 1 copy of the FVL gene. It is much less common in people of color.

What are the symptoms of FVL? — 

Having the FVL gene does not cause symptoms. But if you get a blood clot, that can cause symptoms.

For example, clots can cause:

●Warmth, redness, pain, and swelling in the leg – These are symptoms of a condition called "deep vein thrombosis," or "DVT." This is a blood clot in a vein in the leg.

●Breathing problems, sharp chest pain, coughing, fast heartbeat, and passing out – These are symptoms of a condition called "pulmonary embolism," or "PE." This is a blood clot in the lungs. It usually comes from a blood clot in the leg that breaks off and travels in the bloodstream to the lungs. This can be very dangerous and can even cause death if the clot is large.

Some doctors believe that FVL can also increase the chance of other problems, including stroke, heart attack, or pregnancy loss (miscarriage). But other doctors do not. If there is an increased risk of these conditions, it is very small.

Is there a test for factor V Leiden? — 

Yes. There is a blood test to look for the change in the gene.

If you do have FVL, tell your parents, siblings, and children so they can decide whether to be tested. Their doctor or nurse can help them decide.

If any of these people have FVL, ask your doctor or nurse if you should be tested, too.

How are blood clots treated? — 

Blood clots are treated the same way whether or not the person has FVL.

The main treatment is taking medicine to keep the clot from getting bigger. These medicines are called "anticoagulants." Some people call them "blood thinners," but they do not actually thin the blood. They come as shots or pills. If the clot is severe, doctors sometimes use a stronger medicine that gets rid of clots or do surgery to remove a blood clot in the lungs.

People who had a blood clot usually take a pill medicine to prevent clots for at least 3 months after the clot is found, and often for longer. This medicine helps prevent new blood clots from forming. This is important because people who have a clot often get another one later. Some people have to take the medicine for the rest of their lives.

What can I do to help prevent blood clots? — 

If you are pregnant or need surgery, tell the doctor you have FVL. They will do everything they can to prevent blood clots.

People with FVL should ask their doctor if it is safe for them to take birth control pills or other hormone treatments. The hormones can raise the risk of blood clots. Often, people with FVL should use a different form of birth control (like an intrauterine device, or "IUD") or a different treatment for acne, if needed.

The best way to prevent blood clots is to move your legs often. This keeps the blood moving. Not moving for a long period of time can increase your risk of clots.

Sometimes, you might not be able to move around a lot. Examples include when having surgery, being stuck in bed, or taking a long airplane or car trip.

To prevent a clot during surgery, your doctor can give you an anticoagulant medicine or take other actions to prevent blood clots. If you are having surgery, tell your doctor that you have FVL.

To help prevent a clot on a long trip, you should:

●Stand up and walk around at least once every hour, if you are on a plane or a bus.

●Stop every hour or so to get out and walk around, if you are driving or riding in a car.

●Wear loose, comfortable clothes.

●Change your sitting position and move your legs and feet often.

●Wear knee-high compression stockings, especially if you get leg swelling.

What if I want to get pregnant? — 

People with FVL can have healthy pregnancies. If you have FVL and want to get pregnant, talk to your doctor or nurse. They will work with you to lower your risk of blood clots.

When should I call the doctor? — 

Call for an ambulance (in the US and Canada, call 9-1-1) if you have symptoms of a blood clot in the lungs, such as:

●Breathing problems

●Sharp chest pain

●Coughing

●Fast heartbeat

●Passing out

Call your doctor or nurse right away if you think you might have a blood clot in your leg. Symptoms can include warmth, redness, pain, and swelling.

More on this topic

Patient education: Deep vein thrombosis (blood clot in the leg) (The Basics)
Patient education: Pulmonary embolism (blood clot in the lung) (The Basics)
Patient education: How to give an anticoagulant shot (The Basics)
Patient education: Lowering the risk of a blood clot (The Basics)
Patient education: Prothrombin time and INR (PT/INR) (The Basics)
Patient education: How to take anticoagulants safely (The Basics)

Patient education: Deep vein thrombosis (DVT) (Beyond the Basics)
Patient education: Warfarin (Beyond the Basics)