Factor V Leiden is a common inherited genetic disorder in which your blood has an increased tendency to form clots (thrombophilia), usually in your veins.
Although blood clots can form at any age, for most people the increased risk of clotting doesn’t begin until adulthood. Most people with factor V Leiden never develop abnormal clots. However, some people with factor V Leiden develop clots that lead to long-term health problems or are life-threatening.
Both men and women can have factor V Leiden, but women may have an increased tendency to develop blood clots during pregnancy or when taking the hormone estrogen.
If you have factor V Leiden, medications can lessen your risk of developing blood clots and help you avoid potentially serious complications.
It’s possible to have factor V Leiden without ever developing signs or symptoms. However, 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. Clots can form in your arteries or veins, but with factor V Leiden, they’re much more likely to form in your veins.
Symptoms of a venous clot depend on where it forms and whether and where it travels:
- A clot developing in a deep vein. This is known as deep vein thrombosis (DVT). Signs and symptoms may include pain, significant swelling, redness and warmth in the affected limbs, most commonly your legs, including your ankles and feet.
- A clot that forms closer to the surface of your skin. This is referred to as superficial venous thrombosis, phlebitis or thrombophlebitis. Signs and symptoms usually include warmth, tenderness, pain and redness in the affected area.
- 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. Symptoms may include sudden shortness of breath, chest pain when breathing in, a cough that produces bloody or blood-streaked sputum and rapid heartbeat (tachycardia).
When to see a doctor
See a doctor:
- If your family has a 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.
- If you’ve had one or more blood-clotting incidents without an apparent cause.
- If you develop signs or symptoms of DVT, such as leg pain and swelling.
- If you develop signs or symptoms of a pulmonary embolism, such as chest pain or discomfort. Seek medical attention immediately.
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 form as a result of chemical reactions between specialized blood cells (platelets) and proteins in your blood (clotting factors). Anti-clotting factors control excessive formation of blood clots. One of the clotting proteins is factor V. People with factor V Leiden have a genetic mutation that results in factor V protein responding more slowly to the anti-clotting factors.
In the normal clotting process, anti-clotting proteins combine to help break up factor V to keep it from being reused and forming clots when clotting isn’t needed. However, the factor V Leiden mutation keeps the anti-clotting proteins from breaking down factor V, which keeps it in the blood longer and increases the chance of clotting.
If you have factor V Leiden, you either inherited one copy of the defective gene (heterozygous), which slightly increases your risk of developing blood clots, or you inherited two copies, one from each parent (homozygous), which significantly increases your risk.
The abnormal blood clotting of factor V Leiden can lead to a variety of serious and potentially serious complications, including:
- Pregnancy complications. Although most women with factor V Leiden have normal pregnancies, 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 woman with factor V Leiden and you get pregnant, you’re doctor should monitor you carefully throughout your pregnancy.
- Deep vein thrombosis (DVT). A complication of a deep vein clot can be damage to the valves in the veins in your affected leg, which normally serve to keep the blood flowing upward to your heart. This may result in a condition called chronic venous insufficiency, which causes chronic swelling and discoloration in your lower legs, because of the impaired blood flow.
- Pulmonary embolism. DVT puts you at risk of a clot breaking off and traveling to your lungs or, rarely, your brain. A pulmonary embolism can be fatal, so it’s important to watch for signs and symptoms of a pulmonary embolism and to seek prompt medical attention.
Your doctor may suspect you have factor V Leiden if:
- You have a family history of the disorder
- You’ve had two or more blood-clotting incidents, especially if you’re younger than 50
- You’re a woman who’s had recurrent miscarriages or unexplained pregnancy complications
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 the factor V Leiden mutation. Because appointments can be brief, and because there’s often a lot of ground to cover, it’s a good idea to be well prepared for your appointment. Here’s some information to help you get ready for your appointment, and to know what to expect from your doctor.
What you can do
- Be aware of any pre-appointment restrictions. At the time you make the appointment, be sure to ask if there’s anything you need to do in advance, such as restrict your diet.
- Write down any symptoms you’re experiencing, including any that may seem unrelated to the reason for which you scheduled the appointment.
- Write down your health history, including your history of blood clots. Also include any family history of blood clots or known factor V mutations.
- Write down key personal information, including any major stresses or recent life changes.
- Make a list of all medications, as well as any vitamins or supplements, you’re taking.
- Take a family member or friend along, if possible. It can be difficult to soak up all the information provided to you during an appointment. Someone who accompanies you may remember something that you missed or forgot.
- Write down questions to ask your doctor.
Your time with your doctor is limited, so preparing a list of questions will help you make the most of your time together. List your questions from most important to least important in case time runs out. For factor V Leiden, some basic questions to ask your doctor include:
- What kinds of tests do I need?
- Should I see a specialist? What will that cost, and will my insurance cover seeing a specialist?
- Are there any brochures or other printed material that I can take home with me? What Web sites do you recommend visiting?
If your doctor recommends genetic testing, questions 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?
- Might 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 options for treating the disease if a mutation is found?
- What other family members might be affected?
- How do I broach the subject with them?
- Could this disorder affect my children before they’re grown? Should they be tested?
- What measures are in place to protect my privacy?
- How often have you performed the test?
- How experienced is the lab in performing this test?
- How long will it take to get results back?
In addition to the questions that you’ve prepared to ask your doctor, don’t hesitate to ask questions during your appointment any time you don’t understand something or need more information.
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, it’s likely that you have a mutation in the factor V gene.
- Genetic test. A genetic test either is done as a secondary test to confirm the results of the APC resistance assay or is done alone to determine whether you have a factor V gene mutation. If you’re already taking medication for thrombosis, you’re likely to have only the genetic test because blood-thinning drugs interfere with the activated protein C resistance test. The genetic test also can determine whether you’ve inherited one or two copies of the gene mutation.
Doctors generally use blood-thinning (anticoagulant) medications, such as warfarin (Coumadin), heparin or low molecular weight heparin to treat people who develop blood clots.
If you’ve been tested because of a family history of factor V Leiden, and have not had any blood clots, then your doctor probably won’t prescribe blood thinners unless you’re in a high-risk situation, such as being hospitalized for surgery or other medical reasons. In that case, you may receive preventive doses of blood thinners during your hospital stay.
If you have a thrombosis, 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, but until recently, it had to be administered through a vein and monitored closely. Newer forms of heparin — enoxaparin (Lovenox) and dalteparin (Fragmin) — are known as low molecular weight heparin, which you can inject yourself. Heparin is considered safe to take during pregnancy.
- Warfarin (Coumadin). This anticoagulant comes in pill form, so it’s easier to take than heparin is. Rarely, warfarin can cause birth defects, so it isn’t usually recommended during pregnancy, especially not during the first trimester. A doctor may prescribe warfarin after the first trimester of pregnancy, but only if the benefits of using it outweigh the risks.
Anticoagulation therapy is particularly complex during pregnancy. The therapy is expensive, requires regular injections and carries some significant risks of side effects.
If you’re taking anticoagulant medication, your doctor will monitor your dose with blood tests to be sure your blood is capable of clotting enough to stop your bleeding if you bruise or cut yourself.