What is factor V Leiden?

Factor V Leiden (FVL) is a condition that makes blood more likely to form clots in the legs, lungs, and other parts of the body in some people.

Factor V Leiden is a life-long condition that people are born with. It is caused by an abnormal gene. Parents pass the abnormal gene to their child. Often, people might not know they have the abnormal gene because they don’t have any symptoms.

The “V” is the Roman numeral for “five.” Leiden is a city in Holland where the abnormal gene was discovered.

What are the symptoms of factor V Leiden?

Most people with factor V Leiden never have any symptoms. But some people with factor V Leiden have a higher risk of getting blood clots, especially in the leg or the lungs. When clots do occur, they 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 deep inside the leg.
• Breathing problems, sharp chest pain, coughing, and fast heartbeat – These are symptoms of a condition called “pulmonary embolism.” This is a blood clot in the lungs. It usually comes from a blood clot in the leg that breaks off and travels to the lungs. This can be very dangerous and even cause death if the clot is large.

Some doctors believe that factor V Leiden can also increase the chance of other problems, including stroke, heart attack, or miscarriage (when a pregnancy ends on its own before the baby can live outside the womb). But other doctors do not. If there is an increased risk of these conditions, it is a small increase.

Should I see a doctor or nurse?

See your doctor or nurse right away if you think you might have a blood clot in your leg. If you have symptoms of a stroke or a blood clot in the lungs, call for an ambulance (in the US and Canada, dial 9-1-1). These conditions are very serious and can be life-threatening. Signs of a stroke include drooping of 1 side of the face, arm weakness, and trouble speaking normally.

If one of your relatives has been told that they have factor V Leiden, you can talk to your doctor or nurse to find out if you should be tested.

Is there a test for factor V Leiden?

Yes. If your doctor or nurse thinks you might have factor V Leiden, they can order a blood test to look for the abnormal gene.

If you do have factor V Leiden, you can tell your relatives (parents, siblings, or children) so they can decide whether to be tested. Their doctor or nurse can help them make this decision.

How is factor V Leiden treated?

If factor V Leiden causes a blood clot, the main treatment is medicines that keep the clot from getting bigger. Some of these medicines come in shots and others come in pills. Doctors sometimes use a stronger medicine that gets rid of clots or do surgery to remove a blood clot in the lungs if it is very severe.

People who have had a blood clot usually take a medicine in pill form to prevent clots for at least 3 months after the clot is found, and often for longer. This medicine helps keep new blood clots from forming. It is important because people who have one clot often have another later on.

Is there anything I can do to prevent blood clots?

Yes. The best thing you can do is move your legs often. This keeps the blood moving. Not moving for a long period of time can increase your risk of clots. Examples are having surgery, being stuck in bed, or taking a long airplane or car trip.

To help prevent a clot on a long plane or car ride, you can:

• Stand up and walk around every hour or 2 (or if driving, take breaks often)
• 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

Women with factor V Leiden should ask a doctor or nurse if it is safe to take birth control pills or other hormone treatments. The hormones raise the risk of blood clots. This can be dangerous for women with factor V Leiden.

If you are having surgery, let your doctor know you have factor V Leiden. They will decide if you need medicine or other precautions to prevent blood clots.

What if I want to get pregnant?

If you have factor V Leiden and want to get pregnant, talk to your doctor or nurse. You will be monitored for blood clots during your pregnancy and after the birth. You might also get medicine to help lower the risk of blood clots.