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Should I be tested for Factor V Leiden?

The Controversy and Debate On Testing For Factor V Leiden

Testing for Factor V Leiden in asymptomatic individuals is controversial.

You may be surprised to learn that there is a lot of discussion and debate over the issue of testing for the Factor V Leiden trait.


Testing asymptomatic relatives (someone who shows no symptoms or history of having Factor V Leiden) of venous thrombosis (VTE) patients for Factor V Leiden and other inherited thrombophilia is highly controversial. Most guidelines recommend that requests be considered on a case-by-case basis.


The issue becomes complicated because receiving a positive or negative result from a Factor V Leiden test, depending on the circumstances and motivation behind taking the test, can sometimes create more questions than answers and offer limited help in determining a treatment.


One of the key issues related to the controversy is that there is limited evidence that preventive measures (the use of medications such as blood thinners) is helpful in preventing a future venous blood clot. The risks of “overtreating” an asymptomatic individual and causing excessive bleeding issues can sometimes outweigh the benefits of possibly preventing a blood clot in the future.


On the other hand, someone who knows they have Factor V Leiden has an increased awareness of blood clot symptoms and those things that can trigger a blood clot. They can make better, healthier lifestyle choices to reduce their risk of getting a blood clot.


Factor V Leiden is easily tested for and identified. The sense of fear, lack of control and potentially devastating consequences of a blood clot are strong motivators for families and practitioners who may believe that testing and knowledge will mitigate risk.


Some argue that for people with a single Factor V Leiden gene mutation, the chances of developing a blood clot are fairly low so why test for the disorder. On the other hand, if several people in your family have experienced problems with blood clots and you suspect it could be related to Factor V Leiden, then knowing for sure you have it could help with decisions about lifestyle choices, discussing preventative measures for upcoming surgeries or travel, planning for birth control or hormone replacement therapy treatments, pregnancy, etc. Knowledge is power and sometimes taking some very simple steps toward prevention can possibly save one’s life. Conversely, if one has no symptoms and leads a relatively healthy lifestyle, a positive test result may create additional anxiety or possibly affect insurance coverage. Also, screening asymptomatic individuals of any age, but especially children, may result in overtreatment and bleeding issues rather than blood clot prevention.

According to the experts, when to test for Factor V Leiden can be a complicated question.

The recent introduction of “direct-to-consumer” genetic DNA testing kits from companies like 23andMe has also added fuel to the debate. 


More and more is being discovered every day about Factor V Leiden. New anticoagulation medications are changing the way Factor V Leiden is treated. New medical and genetic research is now uncovering new events that can trigger blood clots and revealing new medical conditions that are related to Factor V Leiden that were previously unknown or even hypothesized. Physicians and genetic counselors face education challenges that simply did not exist a decade ago.


As a result, the official testing guidelines continue to change as more and more research is being published.

The association recognizes that testing for Factor V Leiden in asymptomatic individuals (those not showing any signs or symptoms that they may carry the gene mutation) is debatable and acknowledges and respects the arguments put forth by all sides on this issue. There are definite pros and cons when one is considering whether or not to be tested. We have listed some of these arguments for and against testing below to give you a better understanding of some of the issues.


As always, the American Factor V Leiden Association recommends that you consult with your healthcare professional or genetic counselor to help you in deciding whether to be tested. They can help you interpret the results, explain your risks should you test positive, and make any necessary changes to your plan of care if needed.

The test to see if you have Factor V Leiden is not intrusive and one that your healthcare professional can perform with a simple blood test or you can test for Factor V Leiden yourself via one of the “direct-to-consumer” DNA testing kits as we mentioned.


Ultimately, for those who do not fall within the current testing guidelines and testing is not recommended, deciding whether to be tested for Factor V Leiden is a personal decision.

What are the current guidelines for testing for Factor V Leiden?

Most in the medical community agree on the guidelines below for testing considerations:

  • those who have a venous thrombosis (blood clot) under the age of 50
  • those who have recurrent venous thrombosis
  • those with a family history of venous thrombosis
  • those who have a venous thrombosis in an unusual location such as in the hepatic, mesenteric, and cerebral veins
  • female smokers who suffered myocardial infarction under the age of 50
  • venous thrombosis in pregnant women
  • women with recurrent pregnancy loss, unexplained severe preeclampsia, placental abruption, or intrauterine fetal growth restriction.


Some agree that testing may also be considered in the following situations:

  • those who have a venous thrombosis over the age of 50 except when active malignancy is present.
  • relatives of individuals known to have Factor V Leiden when knowledge that they have Factor V Leiden may influence management of pregnancy and may be a factor in decision-making regarding oral contraceptive use.
  • when knowledge of the Factor V Leiden carrier status may influence management of future pregnancies.

Some testing guidelines from others in the medical community can vary slightly depending on the organization, the source of the data being used, etc.

The College of American Pathologists (CAP) recommends thrombophilia testing for pediatric patients with a personal history of VTE or arterial thrombosis and the consideration of testing of their siblings.


The National Center for Biotechnology (NCBI), U.S. National Library of Medicine states the growing consensus is that Factor V Leiden testing should not be performed on a routine basis and should only be considered when the results will affect clinical management.


The Society for Maternal-Fetal Medicine suggests that women with histories of pregnancy loss, intrauterine growth restriction (IUGR), preeclampsia and abruption should not be tested because the scientific data supporting an association between Factor V Leiden and adverse pregnancy outcomes, such as recurrent pregnancy loss, severe preeclampsia and IUGR is lacking.


What are some issues that should be considered when deciding to be tested for Factor V Leiden?

Arguments FOR being testing for Factor V Leiden:

  • The only way to know if you are at risk for venous blood clots related to Factor V Leiden is to get tested. There are no early symptoms or warning signs. Factor V Leiden does not display any symptoms that you would be able to detect to suggest that you have the disorder. The first indication that you may have the Factor V Leiden mutation is AFTER you develop a venous blood clot.
  • By not knowing you have Factor V Leiden, you could unknowingly do those things that, combined with Factor V Leiden, are known to greatly increase your risks of “triggering” a venous blood clot.
  • Venous blood clots related to Factor V Leiden can kill or cause health-related issues that can last for the rest of your life.
  • If you have Factor V Leiden, you can pass the genetic disorder on to your children and expose them to the same risks of venous blood clots.
  • If you have the more dangerous homozygous type of Factor V Leiden, there is a 100% chance you will pass Factor V Leiden on to your children. Your child will either have the heterozygous or homozygous type, depending on whether the gene passed down from his or her other parent is normal (Factor V) or abnormal (Factor V Leiden).
  • Lack of testing misses those individuals who carry the more serious homozygous type of Factor V Leiden and thus they are unaware of the much greater risks they have of developing a venous blood clot.
  • Testing to find out if you have Factor V Leiden allows you to get counseling about risk factors and “triggers” and use that knowledge to make any lifestyle changes to reduce your risks. Something as simple as getting up and walking during a long plane trip could save your life.
  • Knowing you have Factor V Leiden increases your risk perception making you more aware of the signs and symptoms of blood clots and getting help sooner.
  • Knowing and informing your healthcare professional that you have Factor V Leiden will allow him or her to make better and more informed decisions about your health and be proactive when it comes to surgeries or medical procedures that increase the risk for blood clots.
  • Knowing you have Factor V Leiden allows you to educate your direct relatives (parents, brothers, sisters, children, etc.) about the disorder and allow them the opportunity to get tested should they so desire.
  • A recent consumer experience study in 2020 showed that a large percentage of consumers who discovered they carry the Factor V Leiden genetic disorder were positive about having that knowledge and some took steps to reduce their risks of blood clots and to notify other family members who could benefit from knowing about Factor V Leiden.

Arguments AGAINST being tested for Factor V Leiden:

  • Knowing that Factor V Leiden is present typically does not change the overall recommendations and treatment of a venous blood clot.
  • It was observed in one study that Factor V Leiden testing may incorrectly influence decision-making about how long an anticoagulation medication should be given. The study attributed these wrong decisions to several factors, such as lack of knowledge of current guidelines, incorrect estimation of the risk of a recurrent venous blood clot and poor understanding of the indications for indefinite treatment. The study emphasized the importance of finding a healthcare professional who is knowledgeable about the latest findings and recommendations concerning Factor V Leiden.
  • The downside of testing family members is that finding the gene mutation may lead to unwarranted anxiety, to withholding certain treatments (such as birth control pills), and possibly to discrimination when it comes to purchasing life insurance.
  • A negative test result may lead to a false sense of security and induce family members to ignore other risk factors for blood clots.
  • There is the possibility of over treating asymptomatic individuals to the point that the risk of bleeding outweighs the risk of a venous blood clot.
  • There is the possibility that unintended information is derived from the test such as paternity issues being identified should family testing be pursued.
  • Sometimes the severity of Factor V Leiden can be unrealistically overstated in someone’s mind and cause negative psychological effects. Some individuals do not cope well with negative news and may deter them from making positive lifestyle changes due to a fatalistic attitude.

If my test comes back positive, should my family members be tested?

If you receive positive results for Factor V Leiden from a home DNA testing kit, we recommend that you contact your healthcare professional and genetic counselor and let them know as soon as possible. Together you can review the results and make any changes to your current plan of care.


Most recommend that family members of people with Factor V Leiden discuss the implications of being tested with their healthcare professional, genetic counselor, or a hematologist before they are tested. It is always a good idea for asymptomatic family members of a person who has had a DVT or PE to be counseled about reducing risk factors whether or not Factor V Leiden or other hereditary thrombophilia is present.


Women in families with Factor V Leiden might consider being tested if decisions about birth control or hormone replacement therapy are being made.

Final thoughts on Factor V Testing

Knowledge is Power – Better Education for Patients and Families

Genetic counselors have an essential role in helping physicians, patients and families navigate the pros and cons of testing. Despite the recommendations not to test, many physicians test for Factor V Leiden in an effort to prevent thrombosis related morbidity. Additionally, direct-to-consumer genetic testing has led to many patients bringing test results to physicians. It’s important that they have the resources and education to appropriately counsel these patients and families about guidelines for further testing and risk.

The American Factor V Leiden Association is working hard to promote public awareness, provide education and to be a resource of knowledge.

Our current program initiative on testing is aimed at improving testing guidelines by taking a common sense approach and looking at all variables related to the disorder.

The American Factor V Leiden Association hopes to publish an in-depth position statement on Factor V Leiden testing in the coming months.

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