Factor V Leiden is a mutation of one of the clotting factors in the blood called factor V. This mutation can increase your chance of developing abnormal blood clots (thrombophilia), usually in your veins.
Most people with factor V Leiden (FAK-tur five LIDE-n) never develop abnormal clots. But some do develop clots that lead to long-term health problems or become life-threatening.
Both men and women can have factor V Leiden. Women may have an increased tendency to develop blood clots during pregnancy or when taking the hormone estrogen.
If you have factor V Leiden and have developed blood clots, anticoagulant medications can lessen your risk of developing additional blood clots and help you avoid potentially serious complications.
Most people who have factor V Leiden never develop signs or symptoms. The first indication that you have the disorder may be the development of a blood clot (thrombosis).
Some clots do no damage and disappear on their own. Others can be life-threatening. Symptoms of a blood clot depend on where it forms and whether and where it travels.
A clot in a deep vein
This is known as deep vein thrombosis (DVT). Deep vein thrombosis may not cause any symptoms. If signs and symptoms do occur, they commonly affect your legs, including swelling of your ankles and feet. Other signs and symptoms may include:
- Significant swelling
A clot closer to the surface of your skin
This is referred to as superficial venous thrombosis, phlebitis or thrombophlebitis. Signs and symptoms usually include:
- Tenderness or pain, often in or around the vein with the blood clot
A clot that travels to your lungs
Known as a pulmonary embolism, this occurs when a deep vein clot breaks free and travels through the right side of your heart to your lung, where it blocks blood flow. This can be a life-threatening situation. Signs and symptoms may include:
- Sudden shortness of breath
- Chest pain when breathing in
- A cough that produces bloody or blood-streaked sputum
- Rapid heartbeat (tachycardia)
When to see a doctor
Seek medical attention immediately if you:
- Have signs or symptoms of a pulmonary embolism, such as chest pain or discomfort.
- Have signs or symptoms of deep vein thrombosis, such as leg pain and swelling.
See a doctor if you:
- Have a family history of blood clots or if family members have factor V Leiden. Ask your doctor about the risks and benefits of genetic testing for the disorder.
- Have had one or more blood-clotting incidents without an apparent cause, especially if you're under 50.
A blood clot (thrombus) normally forms to stop the bleeding when an artery or vein is damaged, such as when you experience a cut. Clots are formed by chemical reactions between specialized blood cells (platelets) and proteins in your blood (clotting factors). Anti-clotting factors prevent an excessive formation of blood clots.
Normally, factor V is a clotting protein. Anti-clotting proteins break up factor V, keeping it from forming clots when clotting isn't needed.
Factor V Leiden makes it harder for anti-clotting proteins to break up factor V. This keeps factor V in the blood longer and increases the chance of clotting.
If you have factor V Leiden, you inherited either one copy (heterozygous) or, rarely, two copies (homozygous) of the defective gene. Inheriting one copy slightly increases your risk of developing blood clots. Inheriting two copies — one from each parent — significantly increases your risk of developing blood clots.
A family history of factor V Leiden increases your risk of inheriting the disorder. The disorder is most common in people who are white and of European descent.
Factor V Leiden can be associated with a variety of serious and potentially serious clotting complications, including:
- Pregnancy complications. Most women with factor V Leiden have normal pregnancies. But the mutation has been linked with an increased risk of miscarriage and possibly other complications during pregnancy, including pregnancy-induced high blood pressure (preeclampsia), slow fetal growth and early separation of the placenta from the uterine wall (placental abruption). If you're a pregnant woman with factor V Leiden, be sure your doctor monitors you carefully throughout your pregnancy.
- Deep vein thrombosis (DVT). People with factor V Leiden have an increased risk of developing deep vein thrombosis compared with someone without the mutation, though the overall risk of developing deep vein thrombosis is still low.
- Pulmonary embolism. Deep vein thrombosis puts you at risk of a clot breaking off and traveling to your lungs or, rarely, your brain. A pulmonary embolism can be fatal. It's important to watch for signs and symptoms of a pulmonary embolism, such as shortness of breath or chest pain, and to seek prompt medical attention.
Your doctor may suspect you have factor V Leiden if:
- You have your first blood clotting incident before age 50
- You have a family history of the disorder
- You've had two or more blood-clotting incidents
- You're a woman who has had recurrent miscarriages or unexplained pregnancy complications
- You've had blood clots in unusual areas, such as your liver or brain
Your doctor may refer you to a specialist in genetic disorders (geneticist) or a specialist in blood disorders (hematologist) for testing to determine whether the cause of your blood clots is genetic and, specifically, whether you have factor V Leiden.
Here's some information to help you prepare for your appointment.
What you can do
- List any symptoms you're experiencing, including any that may seem unrelated to the reason for which you scheduled the appointment.
- List your health history, including your history of blood clots. Include any family history of blood clots or known family members with factor V Leiden.
- Make a list of all medications, vitamins or supplements you're taking, along with the dose for each.
- List questions to ask your doctor.
For factor V Leiden, some basic questions to ask your doctor include:
- What kinds of tests do I need?
- Do I need to see a specialist?
- Does my factor V Leiden need to be treated?
- Do I need to take medication to prevent additional blood clots?
- What types of side effects can I expect from the medication?
- Do I need to limit my activity in any way?
- If I have children, do they need to be tested?
- Do you have any brochures or other printed material that I can take with me? What websites do you recommend?
If your doctor recommends genetic testing, some questions you might want to ask the genetic specialist include:
- How accurate is this test?
- What are the risks of the test?
- What information will come out of the test?
- What will a positive or negative result tell me?
- Can the results of the test affect my ability to obtain health insurance?
- Is an uncertain result possible, and what would that mean?
- What are my treatment options if a mutation is found?
- Could other family members be affected?
- Should my children be tested?
- What measures are in place to protect my privacy?
- How experienced is the lab at performing this test?
- How long will it take to get results back?
Your doctor will likely suspect factor V Leiden if you've had one or more episodes of thrombosis or pregnancy loss or if you have a strong family history of thrombotic disease. Your doctor can confirm that you have factor V Leiden with a blood test. Two types of tests can be done:
- Activated protein C resistance test. Your blood sample may be tested to determine whether your blood is resistant to activated protein C, one of the anti-clotting proteins that help control factor V. This is known as an activated protein C (APC) resistance assay. If your blood is resistant to activated protein C, you likely have a mutation in the factor V gene.
Genetic test. A genetic test is done to determine whether you have a factor V gene mutation. It may also be used to confirm the results of the APC resistance test or to determine whether you've inherited one or two copies of the gene mutation.
If you're taking blood-thinning medications (anticoagulants), you may have only the genetic test. Anticoagulants interfere with the activated protein C resistance test.
Testing babies before or soon after birth isn't recommended. Children who don't have symptoms of clotting problems also don't need screening. Blood clots are rare, even in children with factor V Leiden. Testing isn't recommended until adulthood.
When your child is an adult, he or she will be better able to fully understand the risks and benefits associated with genetic testing. Chances are good that your child may never have any signs or symptoms related to factor V Leiden.
Doctors generally use blood-thinning (anticoagulant) medications, such as warfarin (Coumadin, Jantoven), heparin or low molecular weight heparin to treat people who develop blood clots.
If genetic tests have confirmed that you have factor V Leiden, but you haven't had any blood clots, then your doctor probably won't prescribe blood thinners on a regular basis. But you may be given a course of blood thinners to reduce your risk of DVT during high-risk situations, such as having surgery or being hospitalized.
If you have a blood clot, standard initial treatment involves a combination of heparin and warfarin. Your doctor will discontinue the heparin after the initial treatment and continue the warfarin. How long you need to take medication will depend on the circumstances of your thrombosis.
Heparin. This anticoagulant medication works more quickly than warfarin does. It can be administered directly into a vein (intravenously) or under the skin (subcutaneously). You can inject yourself with some forms of heparin, including enoxaparin (Lovenox) and dalteparin (Fragmin). Heparin is considered safe to take during pregnancy.
Possible risks of heparin include excess bleeding and allergic reaction. Heparin doesn't have a standard dose, so it requires regular blood tests and adjustments to get the right dose for you.
Warfarin (Coumadin, Jantoven). This anticoagulant comes in pill form, so it's easier to take than heparin. Warfarin may cause birth defects, so it isn't usually recommended during pregnancy, especially the first trimester. Bleeding is the most common side effect of warfarin.
This drug interacts with many other medications and herbs, so be sure to check with your doctor or pharmacist before taking anything else. As with heparin, there isn't a standard dose for warfarin, so you'll need regular blood tests and dose adjustments while taking warfarin.
New oral blood thinners
Three new oral medications have been approved by the Food and Drug Administration for the prevention and treatment of blood clots in certain people. They have an advantage over warfarin, as they don't require blood test monitoring or dose adjustments. Bleeding complications are the most serious side effect of these medications, but that risk appears to be lower with these drugs than with warfarin:
- Dabigatran (Pradaxa)
- Rivaroxaban (Xarelto)
- Apixaban (Eliquis)
Excessive bleeding caused by these new oral blood thinners can't be easily reversed. Bleeding caused by heparin and warfarin, on the other hand, can be quickly reversed.
These newer medications also haven't been well-studied in pregnant women. They may interact with certain medications, but do have far fewer food or drug interactions compared with warfarin.
Talk with your doctor about the risks and benefits for you of new oral blood thinners compared with warfarin.
If you're taking an anticoagulant medication that increases the risk of excessive bleeding, your doctor will follow you closely. You'll have blood tests to help your doctor make sure your blood is capable of clotting enough to stop bleeding if you bruise or cut yourself.
Factor V Leiden during pregnancy
Most women with factor V Leiden have normal pregnancies. However, the risk of blood clots during pregnancy is higher. Pregnant women with factor V Leiden need close medical supervision throughout their pregnancies. There's no evidence that preventive treatment with blood-thinning medications would be effective enough to outweigh the potential risks of using these drugs during pregnancy or delivery.
If you have factor V Leiden, avoiding certain situations might help reduce your risk of developing blood clots. These include:
Uninterrupted long car or airline trips. When your legs remain still for long periods — more than two hours — your calf muscles don't contract, which normally helps blood circulate.
If you can, try to move around whenever possible on a plane. Drink extra water to prevent dehydration, and avoid alcohol. On a car trip, take periodic breaks and walk around.
If you sit for long periods of time for any reason, get up periodically and stretch your legs.
- Prolonged bed rest, such as during a long illness, or paralysis. Your doctor may suggest the use of compression stockings to keep the blood in your legs moving.
- Injury or surgery. Injury to your veins or surgery can slow blood flow, increasing the risk of blood clots. General anesthetics used during surgery can dilate your veins, which can increase the risk of blood pooling and then clotting. Let your doctor know that you have factor V Leiden.
- Oral contraceptives or estrogen replacement therapy. Because these medications can increase the risk of blood clots on their own, be sure to discuss the risks and the benefits of estrogen-containing medications with your doctor if you have factor V Leiden.
- Being overweight or obese. Being overweight increases the pressure in the veins in your pelvis and legs. Losing weight can lower your risk.
- Smoking. Smoking affects blood clotting and circulation. If you're a smoker, take steps to quit.
One situation you don't have to avoid if you have factor V Leiden is donating blood. People with factor V Leiden can usually donate blood if interested in doing so.
If you're taking blood-thinning medications, you can't donate blood until those medications are fully out of your system. If you've taken blood thinners, check with your doctor before donating blood.
Preventing excessive bleeding
If your factor V Leiden requires you to take anticoagulant medication, here are some steps that might help you prevent injury and avoid excessive bleeding:
- Avoid playing contact sports or engaging in other activities that could result in physical injury. Regular noncontact exercise, such as walking or swimming, is still recommended for good health.
- Use a soft toothbrush and waxed floss.
- Avoid shaving cuts by using an electric razor.
- Be cautious with household tasks involving knives, scissors and other sharp tools.