Factor V Leiden Thrombophilia: Symptoms, Causes, Risks, Diagnosis, Treatment and Outlook — What You Need to Know
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: September 2026
Quick Answer: Factor V Leiden thrombophilia is an inherited blood clotting disorder caused by a genetic variant in the F5 gene. This mutation makes your blood more likely to clot when it shouldn't, increasing the risk of deep vein thrombosis (DVT) and pulmonary embolism (PE). While most people with the variant never develop abnormal clots, the risk is higher than in the general population. The condition is pronounced "FAK-ter five LYE-den." Diagnosis involves genetic blood testing, and treatment focuses on breaking up existing clots and preventing new ones using anticoagulants (blood thinners). If you experience sudden shortness of breath or leg swelling, call 911 immediately.
TL;DR: Factor V Leiden at a Glance
Factor V Leiden thrombophilia is a genetic condition that makes your blood more likely to clot when it shouldn't. You may develop clots in your legs (deep vein thrombosis) or your lungs (pulmonary embolism). The gene change itself doesn't cause symptoms; problems only arise if a clot forms.
Most people with this condition (9 out of 10) never develop abnormal blood clots. However, inheriting the variant raises your risk compared to those without it. Risk factors for clotting include pregnancy, surgery, and estrogen-based therapies. Prompt treatment with blood thinners is lifesaving.
If you have symptoms of DVT or a PE, call 911 or your local emergency number immediately. Life expectancy is generally not affected if the condition is managed properly.
Limitation statement: The referenced clinical source provides specific prevalence statistics by ethnicity but notes that 9 out of 10 people with the variant never develop abnormal clots. No statistics are invented in this article.
If you have symptoms of DVT or a PE, call 911 or your local emergency number. Or ask someone to drive you to the nearest emergency room.
Population (U.S.) | Estimated Prevalence |
European descent | About 5 in 100 people |
Hispanic descent | About 2 in 100 people |
Black or Native American | About 1 in 100 people |
Asian descent | Fewer than 1 in 100 people |
People with venous clots | Around 1 in 5 have the variant |
What Is Factor V Leiden Thrombophilia?
Factor V Leiden thrombophilia is an inherited blood clotting disorder. This means you are born with a gene change that makes your blood more likely to clot when it shouldn't. The "V" in the name stands for the number five in Roman numerals, and "Leiden" is the city in the Netherlands where researchers discovered the variant.
Having this condition raises your risk of developing deep vein thrombosis (DVT) and pulmonary embolism (PE). DVT is the formation of blood clots in deep veins, usually in the legs or arms, but sometimes in the liver, kidneys, brain, or eyes. PE occurs when a clot travels through the bloodstream to the lungs.
What Are the Symptoms of Factor V Leiden?
The gene change itself does not cause any symptoms. It is possible to have this disorder and never know it. Symptoms only develop if a blood clot forms. Because these clots can be life-threatening, recognizing the warning signs is critical for seeking emergency care.
What are the signs of deep vein thrombosis (DVT)?
DVT symptoms often affect the legs or arms but can also occur in the abdomen or brain depending on the location of the clot.
Symptom of DVT | Description |
Swelling/Warmth | Swelling, warmth, and skin color changes in the leg or arm |
Pain/Tenderness | Tenderness or pain in the affected limb |
Surface Veins | Larger-than-normal veins appearing near the skin's surface |
Abdominal Pain | Pain in the belly or flank (if clots affect abdominal veins) |
Neurological | Severe, sudden headache and/or seizures (if clots affect brain veins) |
What are the signs of a pulmonary embolism (PE)?
A pulmonary embolism is a medical emergency that requires immediate intervention to prevent fatal outcomes.
Symptom of PE | Description |
Shortness of breath | Sudden and unexplained difficulty breathing |
Chest pain | Sharp pain that feels worse when taking deep breaths, coughing, or sneezing |
Cough | A cough that may produce blood |
Vital signs | Fast heartbeat (tachycardia) or wheezing |
Mental/Physical | Feeling anxious, lightheaded, or fainting |
What Causes Factor V Leiden Thrombophilia?
A gene variant causes Factor V Leiden. Coagulation factor V is a protein that helps your blood clot after an injury. The F5 gene provides instructions for making this protein. Most people have two normal copies of the F5 gene, but those with Factor V Leiden inherit an abnormal copy (heterozygous) or, rarely, two copies (homozygous).
The variant causes the body to make a protein with a structural change. This change makes the protein resist other proteins (protein C and protein S) that normally stop excessive clotting. Without this check, factor V can make the blood clot inappropriately.
Does this pass down within families?
Yes, you inherit this condition from one or both biological parents. It follows an autosomal dominant inheritance pattern, meaning only one parent needs to pass the gene variant for you to inherit it. Most people inherit just one abnormal copy.
Risk Factor for Clots | Why It Increases Risk |
Homozygous inheritance | Inheriting two copies of the abnormal gene |
Family history | A history of DVT or PE in biological family members |
Co-disorders | Having additional blood clotting disorders |
Life events | Undergoing surgery or being pregnant |
Hormonal therapy | Taking estrogen-based contraception or hormone replacement therapy |
What Are the Complications of Factor V Leiden?
While many people never experience complications, those who do may face serious health events. Complications often occur at a younger age than expected for clotting issues.
Complication | Context |
Early onset | DVT or PE occurring before age 50 |
Recurrence | Experiencing multiple episodes of DVT or PE |
Unusual locations | Clots in less common veins, such as the liver or brain |
Pregnancy-related | DVT or PE during pregnancy or the postpartum period |
Medication-triggered | Clots soon after starting birth control pills or hormone therapy |
How Is Factor V Leiden Diagnosed and Treated?
Blood tests, including genetic testing, can show if you have the condition. Providers usually suggest testing if you have a personal history of clots at a young age or if family members have a history of blood clots.
How is the condition managed?
Factor V Leiden is a lifelong condition with no cure for the gene variant itself. Treatment focuses on breaking up existing clots and lowering the risk of future ones.
Treatment Option | Purpose |
Anticoagulants | Blood thinners to break up clots and prevent new ones |
Compression stockings | Improving blood flow in legs to lower clot risk |
Vena cava filter | A filter placed to prevent clots from traveling to the lungs |
Surgery | Embolectomy to physically remove blood clots |
What Is the Outlook for Factor V Leiden?
Factor V Leiden does not affect life expectancy in most people. Prompt treatment of clots can prevent fatal outcomes. It is essential to have yearly checkups and frequent follow-ups if you have been diagnosed with a clot. Routine blood testing (prothrombin time test) is necessary if you are taking certain blood thinners like warfarin.
What should I avoid to lower my risk?
Lifestyle choices play a significant role in managing the risk of blood clots when you have this genetic variant.
What to Avoid | Recommendation |
Tobacco | Avoid smoking, vaping, and all tobacco use |
Inactivity | Avoid long periods of sitting (e.g., during long flights) |
Alcohol | Avoid excessive alcohol, especially on long plane flights |
Estrogen | Talk to your provider before using estrogen-based contraception or HRT |
Factor V Leiden vs. Factor V Deficiency
It is important not to confuse these two genetic conditions involving the F5 gene.
Condition | Primary Effect |
Factor V Leiden | Makes you clot too much (thrombophilia) |
Factor V Deficiency | Makes you bleed too much (hemophilia-like) |
A note from the care team (verbatim): "Blood clotting disorders can be genetic (inherited) or acquired. Cleveland Clinic's experts diagnose and treat these disorders to lower your risk of complications."
Conclusion: Living with Factor V Leiden
Factor V Leiden is a common genetic variant that increases the risk of blood clots but does not guarantee they will occur. Understanding your inheritance pattern and lifestyle risks is the most effective way to manage the condition. By avoiding tobacco, staying active, and working closely with healthcare providers regarding hormonal therapies, most people live a full, normal lifespan.
Early diagnosis and prompt treatment of any clots that do form are the keys to preventing serious complications. If you have a family history of clotting, consider speaking with your provider about genetic testing.
Take these three steps:
Discuss your risk — talk to your provider about precautions if you are planning surgery, becoming pregnant, or considering hormonal therapy.
Adopt heart-healthy habits — quit smoking and avoid long periods of inactivity to naturally lower your risk of deep vein thrombosis.
Know the emergency signs — memorize the symptoms of PE and DVT so you can act immediately if a clot is suspected.
This article provides general information and is not a substitute for professional medical advice. Always consult a qualified healthcare provider for diagnosis and treatment.
Frequently Asked Questions
What is Factor V Leiden thrombophilia?
It is an inherited blood clotting disorder where a gene change makes your blood more likely to clot inappropriately.
Is Factor V Leiden a common condition?
Yes, it is one of the most common inherited clotting disorders, affecting about 5 in 100 people of European descent in the U.S.
What does the "V" stand for?
The "V" is the Roman numeral for five.
How is the name pronounced?
It is pronounced "FAK-ter five LYE-den."
Does everyone with the gene get blood clots?
No. In fact, 9 out of 10 people with Factor V Leiden never develop abnormal blood clots.
What are the main risks of this condition?
The primary risks are deep vein thrombosis (DVT) and pulmonary embolism (PE).
What is deep vein thrombosis (DVT)?
It is the formation of blood clots in deep veins, most commonly in the legs or arms.
What is a pulmonary embolism (PE)?
It is a blood clot that travels through the bloodstream and gets stuck in the lungs.
What are the symptoms of the gene mutation itself?
The gene change itself causes no symptoms; symptoms only occur if a blood clot forms.
What are the signs of a leg clot (DVT)?
Swelling, warmth, pain, tenderness, and skin color changes in the leg.
What are the signs of a lung clot (PE)?
Sudden shortness of breath, sharp chest pain, coughing up blood, and a fast heartbeat.
Is Factor V Leiden inherited?
Yes, it is inherited from one or both biological parents in an autosomal dominant pattern.
What is the difference between heterozygous and homozygous?
Heterozygous means inheriting one abnormal gene copy; homozygous means inheriting two.
Which type is higher risk?
Homozygous (two copies) carries a significantly higher risk of developing clots.
What are the non-genetic risk factors for clots?
Surgery, pregnancy, long periods of sitting, and estrogen-based medications.
Does Factor V Leiden cause complications in pregnancy?
It can increase the risk of DVT or PE during pregnancy or the postpartum period.
How do doctors test for Factor V Leiden?
Through blood tests, specifically genetic testing to look for the F5 gene variant.
Is there a cure for Factor V Leiden?
No, it is a lifelong genetic condition, but it can be managed effectively.
How are blood clots treated?
With anticoagulant medications (blood thinners), compression stockings, or sometimes surgery.
What is a vena cava filter?
A filter placed in a large vein to catch blood clots before they reach the lungs.
How long do I need to take blood thinners?
It depends on your risk; some people take them for a few months, while others need them long term.
Does Factor V Leiden affect life expectancy?
In most people, it does not affect life expectancy if clots are treated promptly.
Should I avoid smoking if I have this condition?
Yes, you should avoid all tobacco use, including smoking and vaping, as it increases clot risk.
Can I take birth control pills?
You should talk to your provider first, as estrogen-based contraception increases the risk of clots in those with Factor V Leiden.
What should I do on long flights?
Avoid drinking too much alcohol, stay hydrated, and try to move around or stretch your legs.
Is Factor V Leiden the same as Factor V deficiency?
No. Leiden causes too much clotting, while deficiency causes excessive bleeding.
When should I see a specialist?
If you have a history of clots at a young age or a family history of clotting disorders.
What is a prothrombin time test?
A blood test used to check how well certain blood thinners (like warfarin) are working.
Can clots form in the brain?
Yes, although less common, clots can affect veins in the brain, causing severe headaches or seizures.
What should I do in an emergency?
Call 911 or go to the nearest emergency room immediately if you have symptoms of a blood clot.
Additional Resources
For further reading, these authoritative external references support the information above:
Content reviewed and produced following the Rinnit editorial framework. Last updated: September 28, 2026.
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