Thrombophilia

Is Testing Right for Me? I Have My Test Results

Thrombophilia

Risk Factors for Venous Thrombosis

Everyone has a chance to have a blood clot sometime in his or her lifetime. Venous thrombosis is usually caused by a combination of factors — not simply genes. Many people with a history of blood clots don't have an inherited thrombophilia. In these cases, clotting is usually caused by a combination of non-genetic risk factors. The more risk factors you have, the higher the chance you will have a blood clot. Some risk factors, like age, cannot be changed, but some can be reduced by lifestyle changes or medical treatments.

Triggering Events
Race and Ethnicity
Age Related Risks

Triggering Events

Many medical conditions, procedures, and other factors increase the chance of clotting. Below are some examples. In general, having a factor V Leiden or prothrombin mutation increases the risk even more than usual.

  • Surgery, although the risks depend in part on the type of surgery, associated trauma, associated immobility, and other factors
  • Other health conditions like injury, infections, and inflammatory diseases increase risk to varying degrees.
  • Cancer and cancer treatments both increase the risk of clotting, but the type of cancer and treatment influences how much the risk is increased.
  • Birth control pills, but some increase the risk more than others do
  • Hormone replacement therapy, but certain therapies increase the risk more than others do
  • Pregnancy, delivery, and the time after pregnancy
  • Long distance travel, particularly that restricts moving around frequently
  • Lifestyle risk factors like a sedentary lifestyle, obesity, and smoking

Race and Ethnicity

A person's race and ethnic background (where that person's ancestors came from) plays an important role in predicting the chance for abnormal clotting. African Americans have the highest chance for having an abnormal blood clot followed by Caucasians and Hispanics. Asians and Pacific Islanders have a particularly low risk for blood clotting compared to other groups, but abnormal clots do still happen.

Age-Related Risks

The chance of having an abnormal blood clot goes up dramatically with age, especially after age 60. For example, children under 15 have less than a 1 in 20,000 chance for clotting. By the fifties, the risk goes up to 1 in 760 to 1600. Those over 80 years old have a 1 in 170 to 220 risk.

Next: Pros and Cons

Why are you considering genetic testing? Check only one at a time.

I have a history of one or more blood clots that could be related to an inherited thrombophilia. (See Who Should Consider Testing if you aren't sure.)

I have a family member with a factor V Leiden and/or prothrombin gene mutation.

I have a family history of abnormal blood clots that could be related to an inherited thrombophilia (usually clots before age 50 or abnormal clotting in more than one generation).

I have had serious pregnancy complications, including miscarriage, stillbirth, placental abruption, severe preeclampsia or fetal growth problems

None of these.

Testing may help explain your clot, but may not change how your doctor treats you.

Factor V Leiden (FVL) and prothrombin G20210A (PT) mutations are more common in people who have had a vein clot. In people who have had their first blood clot, 1 in 5 (20%) have an FVL mutation and 1 in 16 (6%) have a PT mutation.

You have a higher chance of having a factor V Leiden or prothrombin gene mutation if you have had any of the following:

  • A vein clot at a young age, usually before age 50
  • History of more than one vein clot
  • A clot caused by pregnancy, birth control pills, or hormone replacement therapy
  • A clot with no apparent cause (called "unprovoked" or "idiopathic")
  • A clot in an unusual place like veins in the liver, kidneys, gut, and brain

Once a person has a clot, the main concern is preventing another. Most clots are treated with blood thinners and other drugs for some period of time to prevent more clotting — no matter what the reason for the clot is.

Most people with only one mutation have a higher risk of complications from long-term blood thinners than the risk of clotting from the mutation. A factor V Leiden mutation increases your chance for another clot only a little (less than twice the average risk). The prothrombin mutation doesn't seem to increase the risk at all for most people. As a result, experts don’t recommend treating someone with one mutation for longer than usual.

People who have had a clot may be treated differently if they have other higher risk situations in the future, like surgery or pregnancy. Women are also generally advised to avoid certain oral contraceptives, hormone replacement therapy, and other drugs that have estrogen if they have other good options. But again, the treatment recommendations are based on having had a clot already — not having a mutation.

Rarely, a person will have two FVL and/or PT mutations. The risk for clotting is much higher with two mutations. However, this result is so uncommon that most experts don’t think it is worthwhile to test people with a clot to look for two mutations.

Even if the test results don’t change the drugs a person takes to prevent clotting, some people find it useful to know for other reasons. For example, there are other ways to help prevent blood clots that don’t involve medications. Some people may be more conscious of preventing a clot or recognizing it early when they know they have a mutation.

Testing may alert you to a small increased risk for clotting, but may not change how your doctor treats you.

People with a close relative (parent, child, or sibling) who had a blood clot also have a higher risk for clotting — about 2 to 3 times higher than average. A family history of clots at a young age or more than one relative with a clot could mean that a factor V Leiden (FVL) or prothrombin (PT) mutation runs in your family. There are inherited causes of clotting, but they are less common. You should talk to your doctor or a genetic counselor about your family history to understand your risks and whether any testing may be useful.

You have a higher chance of having a factor V Leiden (FVL) or prothrombin (PT) gene mutation if one of your blood relatives has a mutation. Your actual risk depends on how closely you are related to this family member. If you aren’t sure already, try to find out the name of the mutation that runs in your family. If you decide to have testing, this information will help your doctor be sure you get the right test.

Factor V Leiden and prothrombin mutations increase the chance of clotting. The average person has about a 1 in 1000 chance for an abnormal clot each year. People with a FVL mutation have a 3 to 8 times higher chance that average. People with a PT mutation have a 2 to 4 times higher chance. This still means that the chance for a clot is relatively low — no more than a 1 in 125 to 1 in 500 chance each year.

People may also have two FVL and/or PT mutations. Two mutations raises the risk for clotting much more, but is rare.

People who have had a clot, or who have a very high risk, may be treated with drugs that thin the blood, called anticoagulants. However, these drugs have risks. Most people with only one mutation have a higher risk of complications from long-term blood thinners than the risk of clotting from the mutation. Most experts feel that finding a FVL or PT mutation should not change the treatment of someone who has never had a clot.

When people know they have a higher risk for clotting based on their family history, they may be treated differently during higher risk situations, like surgery or pregnancy. Women are also generally advised to avoid certain oral contraceptives, hormone replacement therapy, and other drugs that have estrogen if they have other good options. Generally, it is enough to know that a person has a risk based on their family history. The actual test results for a FVL or PT mutation may not change that treatment.

Although mutation test results usually don’t mean a person needs to take drugs to prevent clotting, some people find it useful to know for other reasons. For example, there are other ways to help prevent blood clots that don’t involve medications. Some people may be more conscious of preventing a clot or recognizing it early when they know they have a mutation.

Testing may not change how your doctor treats you.

There are many causes of serious pregnancy complications, like miscarriage, stillbirth, placental abruption, preeclampsia, and growth problems in the developing baby. An inherited tendency to clot (called thrombophilia) may be related, but studies haven’t agreed.

The factor V Leiden (FVL) and prothrombin (PT) G20210A mutations are two causes of thrombophilia. There are others. See Women and Thrombophilia for more information .

It isn't proven, but researchers suspect that thrombophilia may increase the chance of blood clots in the placenta (afterbirth). The placenta transfers oxygen and nutrients between the mother and developing baby. Clots may block the flow of these substances.

Many women have a FVL or PT mutation and don't have any pregnancy complications. This means a mutation alone does not explain why someone has a pregnancy loss or other complications.

There are drugs available that prevent clots, called blood thinners or anticoagulants. However, these drugs have risks. Experts don’t agree about whether anti-clotting treatment can lower the chance for pregnancy complications in women with a FVL or PT mutation. The risk from the drugs may be higher than the benefits. Studies are being done now to try to figure out if these drugs are useful for some women. Until then, most medical guidelines suggest no anti-clotting treatment for women with a mutation.

Because there is no agreed upon treatment for women with a mutation, and the risks for pregnancy complications are low overall, testing may not be useful.

Testing may not be useful for you.

You didn’t select any of the most common reasons people consider testing. The main signs of a factor V Leiden (FVL) or prothrombin (PT) mutation are discussed in the Who Should Consider Testing section. Even when people have signs that they might have a FVL or PT mutation, testing may still not make sense. The results usually don’t change how a person is treated.

Testing is not recommended for people without any sign that they may have a mutation. For example, even though these mutations raise the chance of clotting in women who take birth control pills, experts specifically don't recommend testing for all women who are considering or taking birth control pills.

If you have a reason for testing that isn't covered here, talk to your doctor or a genetic counselor about whether testing might be useful for you.