Factor V Leiden is also known as FVL. It is a genetic condition that increases the chances of having blood clots. FVL can contribute to Deep Vein Thrombosis (clots in your veins), Pulmonary Embolisms (clots in your lungs), and problems with pregnancy.

A person with FVL has inherited at least one Factor V Leiden gene from a parent. People with FVL can have one or two copies of the gene. One copy of the gene tends to cause less clotting than two copies. You will see one copy referred to as heterozygous and the two gene copy form referred to as homozygous. Heterozygous people will have a 50% chance of passing the FVL gene on to any children. Homozygous people will always pass a gene onto any offspring.

The best test to see if you have FVL is a genetic test. This test can determine if you are heterozygous or homozygous and is accurate when one has clots or is on anti coagulation medication. For these reasons, the genetic test is the most accurate.

Right now there is no cure for Factor V Leiden. Luckily, most people with FVL (90%) NEVER have a clot¹. For those people who do clot, there are very good treatment options to prevent further clots.

Factor V Leiden is a genetic condition. In order to have FVL a person must have at least one parent with the FVL gene. Each person carries a pair of genes for the clotting factor known as Factor V Leiden. One gene comes from the mother and the other gene comes from the father. Factor V Leiden is a dominant gene. This means that if a person has a copy of the gene they WILL have FVL. The Factor V Leiden gene always causes a person to have FVL. The FVL gene doesn't always cause blood clots. A person with at least one FVL gene will have a higher tendency to clot but only 10% of people with FVL will clot. This is why there is a false belief that FVL can "skip" a generation. If you have one FVL gene, you have FVL. If you have FVL your child may also have FVL.

Punnet squares are a way to determine the probability that a person's offspring will have a genetic condition. Take a look at the Punnet Squares below to understand how FVL is inherited. A "n" represents a "normal" gene. A "F" represents a FVL gene. The F is capitalized because it is always dominant. If a person has at least one F they have FVL.

Both parents in this group have normal FVL genes. None of the offspring will have FVL.  100% are normal.

When a person has two copies of the FVL gene this is referred to as homozygous FVL.  This individual has a much higher chance of clotting.  If both parents are homozygous all of the offspring will also be homozygous.  100% will have homozygous FVL.

When a person has one copy of the FVL gene this is referred to as heterozygous.  This is the most common way to inherit FVL.  This group has a 10% chance of a clotting episode.

When one parent has heterozygous FVL and one parents is normal there is a 50% chance that the offspring will be normal and a 50% chance that the offspring will have heterozygous FVL.

When one parent has heterozygous FVL and the other parent has homozygous FVL all of the offspring will have FVL.  50% will have the more serious homozygous FVL.  50% will have the more common, less serious heterozygous FVL.

When both parents have heterozygous FVL 25% of the offspring will be normal and not have FVL.  Another 25% of the offspring will have the more serious homozygous FVL.  50% of the offspring will have heterozygous FVL.

When one parent has homozygous FVL and one parent is normal it is guaranteed that all of the offspring will have FVL.  In this case, 100% of the offspring will have heterozygous FVL.

How does someone find out that he or she has the Factor V Leiden gene? This depends on the reasons for testing.

As FVL is a genetic condition, some doctors recommend having family members tested for FVL. These tests are done before the other family members have symptoms. This testing is very controversial. Testing asymptomatic individuals may cause excess worry, costs money, and may impact the availability of life insurance, The recently passed Genetic Information Nondiscrimination Act (GINA) prevents job or health insurance discrimination. On the other hand, FVL testing will allow individuals to take preemptive measures to prevent clots. Women with FVL could make birth control choices that would be safe with FVL. Also, hormone replacement (in particular estrogen) could be ruled out in order to prevent clots. People who tested positive could also use compression stockings, maintain hydration, and be cautious during travel to prevent clots. These measures could help the 10% of people with FVL who otherwise would clot. As clots can be fatal, this decision may save lives.

If a family decides not to have other members tested, it is still a good idea to share the diagnosis with everyone. Knowing the diagnosis and the possibility of others sharing the gene would allow everyone to take precautions during travel, surgery, or other high risk activities. Also, family members could learn about pulmonary embolisms and deep vein thrombosis. Learning symptoms and warning signs will help family members whether they decide to be tested or not.

Other groups that may be intterested in FVL testing are women who have had multiple miscarriages, individuals with cancer, and individuals who have major lifestyles risks such as people who regularly make long haul, international flights.

There are some people who will have testing recommended by a physician. This may be recommended when:

• The patient has an unprovoked pulmonary embolism before age 40
• The patient has had multiple or recurrent blood clots, deep vein thrombosis, or pulmonary embolism
• The patient has clots and has a family history of thrombophilia
• If the patient has had multiple miscarriages
• If the clot is in an unusual location

There are a number of conditions that can cause clotting. it is important that the doctor does the tests for the full range of thrombophilias. The initial screening for Factor V Leiden will look for activated protein C (APC) resistance. The problem with this test is that anti coagulation therapy will alter the test results. While a patient has clots and/or is receiving anti coagulation therapy this test is not accurate. The other method of testing for Factor V Leiden is a genetic test. This test will look at the DNA to determine if the Factor V Leiden gene is in the correct or the mutated form. Because this test evaluates DNA, it can be done when a patient has an active clot and while a patient is on anti coagulation therapy. Also, this test will be able to determine if an individual has one or two copies of the gene. This is important as it will help to determine the severity of clotting that an individual may experience. An individual with two mutated Factor V Leiden genes has a much higher risk of clotting. For men, the genetic test will also be able to tell the patient whether the mother and/or father were the bearer of the gene.

Based on the results of the testing, the reasons for testing, and the absence or presence of other clotting conditions doctors will decide if and how long a patient will remain on anti coagulation therapy.

Treatment of FVL will depend on if you have had clotting episodes or not. It also will vary based on if you are having problems carrying a pregnancy to term.

For those people who haven't clotted, treatment will typically consist of staying hydrated, being active, and being proactive in times when you might be more prone to clot. Hydration will help your blood flow more easily. Make sure that you are getting plenty to drink especially when out in the heat or in times when you are stationary such as airplane travel. Unlike arteries, veins have no muscles. Blood is returned to your heart using the regular muscles in your body. Staying active will strengthen those muscles and keep blood moving, thus, preventing clots.

People with Factor V Leiden need to take precautions in times when clotting may occur. Some of these times are:

• car or air travel
• sitting still for more than 1 or 2 hours at a time
• being bedridden for any reason
• illness
• surgery
• pregnancy

During these times, If possible, get up every hour and move around. Also, make sure to keep hydrated. If you are at a higher risk due to surgery, illness, or pregnancy speak to your doctor about ways to be safe and clot free.

If you have clotted before it is likely that you will be placed on anti coagulation therapy. Anti coagulation therapy includes drugs such as Coumadin, warfarin, Lovenox, heparin, and low molecular weight heparins. If you have only clotted once and it was with extenuating factors you may only continue anticoagulation therapy for 3 months to a year. Length of treatment will depend on your personal circumstances, health history, if there are other clotting disorders, and your doctor's preferences.

One thing that is important to note is that Coumadin/warfarin is not safe during pregnancy. It will be important to work with your doctor to find a safe alternative that will help both you and your baby be safe and healthy throughout the pregnancy and in the months following delivery.

Please see my other hubs for more detailed information about treatment and medications.