Your Resource for all Things Relating to Factor V Leiden

Should I be tested before starting hormone replacement therapy?

The current recommended testing guidelines relating to Factor V Leiden are as follows:


  • those who have venous thrombosis under the age of 50
  • those who have recurrent venous thrombosis
  • those who have a family history of venous thrombosis
  • female smokers who have suffered myocardial infarction under the age of 50
  • venous thrombosis in pregnant women or those taking oral contraceptives
  • some guidelines include women with recurrent pregnancy loss, unexplained severe preeclampsia, placental abruption as well as intrauterine fetal growth restriction

There are a few situations that are not addressed in the above guidelines that could increase your risk. The guidelines assume that you are in contact with direct family members and are aware of any history of venous blood clots they have experienced. Also, the guidelines do not take into account other major risk factors for blood clots such as hospitalization, surgery, trauma, obesity, smoking, and immobility.

Examining the risks….

Factor V Leiden is the most common genetic cause of primary and recurrent venous thromboembolism in women.

The only way to know if you have Factor V Leiden, or know if you have the heterozygous type or the much more serious homozygous type of Factor V Leiden is to get tested.

The increased risk for blood clots caused by hormone therapy combined with the increased risk for venous blood clots caused by Factor V Leiden should be taken very seriously. 

When entering menopause, experts say women with a history of blood clots should only use estrogen or estrogen and progestin if they are taking anticoagulation or blood thinning medication. For women who are not taking anticoagulants and who have a family history of blood clots or a history of blood clots themselves, hormone therapies increase the risk of potentially life-threatening blood clots.


According to Dr. Andra James, MD, at Duke University, for women who are not taking anticoagulants, but who have had a blood clot or have thrombophilia (like Factor V Leiden), the circumstances that would justify taking postmenopausal hormone therapy are rare or nonexistent.


The good news is that postmenopausal symptoms such as hot flashes, sleeplessness, vaginal dryness and bone loss can be managed without estrogen.


Despite the increased risks, women are not systematically tested for Factor V Leiden before they are prescribed oral contraceptives, before or during pregnancy, or before commencing hormone replacement therapy unless they fall within the guidelines above. The only way to be tested is to request the test from your healthcare professional or utilize one of the direct-to-consumer DNA testing kits now available from companies like 23andMe.


If you are currently on or are considering starting hormone treatment, we strongly recommend that you ask your healthcare professional or genetic counselor if genetic testing for Factor V Leiden should be considered in your situation.


Knowing you have Factor V Leiden could save your life.


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.


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.

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

We hope to publish an in-depth position statement on Factor V Leiden testing in the coming months.

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