Your Resource for all Things Relating to Factor V Leiden

Frequently Asked Questions

Factor V Leiden is a genetic blood clotting disorder caused by a mutation in the gene that controls factor V, a protein needed in blood clotting.

The Factor V Leiden mutation itself does not display any symptoms that you would be able to detect to suggest that you have the disorder prior to developing a blood clot.

Typically, the first indication that you may have Factor V Leiden is when you or someone in your family develops a venous blood clot.

Factor V Leiden is found in both men and women. Women with the condition face an increased risk of developing blood clots because of the hormonal changes brought on by pregnancy or while taking hormone-replacement therapy during menopause.

Typically, treatment for Factor V Leiden is only needed after someone has developed a venous blood clot and includes blood-thinning medications. Sometimes blood-thinning medications are prescribed to someone who hasn’t developed a venous blood clot if the situation warrants (upcoming surgery, major illness, cancer, etc.) in order to decrease the risk of developing a blood clot.

Thrombophilia is defined as an increased tendency to form abnormal blood clots that can block blood vessels.

Factor V Leiden is not a disease but a genetic disorder.

People with Factor V Leiden may donate blood, platelets or plasma safely, as long as they are not on an anticoagulant (blood thinning medication) such as warfarin.

Factor V Leiden should not be confused with Factor V deficiency. Factor V deficiency is an inherited bleeding disorder that can cause excessive bleeding.

No… genetic mutations are passed from generation to generation because we receive our DNA from our parents. 

Different genetic blood clotting disorders have different levels of relationship to miscarriage, but Factor V Leiden is one of the hereditary thrombophilias that does appear to increase the risk of miscarriage. 

Factor V Leiden is the most common inherited form of thrombophilia. Between 3 and 8 percent of people with European ancestry carry one copy of the Factor V Leiden mutation in each cell, and about 1 in 5,000 people have two copies of the mutation. The mutation is less common in other populations.

You are not able to register to donate bone morrow if you have a serious bleeding problem such as hemophilia or Factor V Leiden, or if you have ever had a deep vein blood clot, require anticoagulant medications, have aplastic anemia, or Von Willibrand’s Disease.

Factor V Leiden has been associated with ischemic stroke in children, but not in adults. Further research needs to be done.

Women with Factor V Leiden thrombophilia most often have normal pregnancies. Treatment with an anticoagulant during pregnancy and/or following delivery is often not needed, but may be recommended depending on the woman’s personal and family health history, method of delivery, and other risk factors.

Heterozygous means that the two copies of a gene are different. In this case, one of the Factor V gene codes is for normal Factor V and the other Factor V gene code is for Factor V Leiden.

Factor V Leiden thrombophilia is inherited in an autosomal dominant manner. Homozygosity for the Leiden variant are inherited in an autosomal recessive manner.

There are two types of Factor V Leiden. One is called heterozygous and the other is called homozygous.

If you inherited one Factor V Leiden gene from one parent, you have the heterozygous type of Factor V Leiden. In your body, you have 50% Factor V Leiden and 50% normal Factor V.

If you inherited one Factor V Leiden gene from both parents, you have the homozygous type of Factor V Leiden. In your body, you have 100% Factor V Leiden and 0% of the normal Factor V.

Factor V Leiden thrombophilia is caused by a specific mutation in the Factor V gene.

This mutation can increase your chance of developing abnormal blood clots. Most people with Factor V Leiden never develop abnormal clots. But in people who do, these abnormal clots can lead to long-term health problems or become life-threatening.

There are currently no recommendations suggesting that one be worn. However, depending on your personal situation one may be warranted.

No… MTHFR stands for methylenetetrahydrofolate reductase. The MTHFR mutation is an anomaly in a person’s genetic coding which interferes with the body’s ability to produce MTHFR enzyme. 

A simple blood test (called a screening test) can show if you have Activated Protein C resistance. If you do, another blood test that examines your Factor V gene will be done to find out if Factor V Leiden is the cause of the resistance and what type of Factor V Leiden you have.


Factor V Leiden has been associated with preeclampsia which is high blood pressure during pregnancy. It is also associated with placental abruption or early separation of the placenta from your uterine wall.

  • Given my medical and family history, does my Factor V Leiden need to be treated?
  • Is my Factor V Leiden heterozygous or homozygous?
  • Do I need to see a specialist?
  • Do I need to take medication to prevent new or additional blood clots?
  • If so, what side effects can I expect from the medication?
  • Do I need to change my lifestyle or activity in any way?
  • If I have children, do they need to be tested?
  • Does anyone else in my family need to be tested?
  • What websites do you recommend?

Someone who inherits one copy of the Factor V Leiden gene from one parent and one copy of the normal factor V gene from the other parent is heterozygous for the mutation, and has a 50% chance of having the abnormal gene in his blood. Homozygous Factor V Leiden occurs when both parents pass the mutation to a child, who then is certain to have the abnormal gene in his blood.

People with Factor V Leiden who’ve never had a blood clot won’t be routinely treated with anticoagulation (blood thinning) medications unless there are other medical issues or life events that may warrant it. People with Factor V Leiden who have a history of recurrent blood clotting are generally treated with anticoagulation medications for life.

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