Factor V Leiden

Factor V Leiden, also called factor V Leiden thrombophilia, is one of the most common inherited blood clotting disorders. It changes a clotting protein called factor V, making it harder for your body to naturally stop a clot once it starts forming. This can lead to deep vein thrombosis (DVT), a clot that usually forms in the legs, or pulmonary embolism (PE), a clot that travels to the lungs. It’s different from factor V deficiency, a rare bleeding disorder that makes it harder for blood to clot.

Most people with the factor V Leiden mutation never develop a dangerous blood clot, but knowing you have the condition can help you and your care team take extra precautions during situations that raise your chances of clotting, like surgery, pregnancy, or hormone therapy.

Hematologists diagnose and manage blood clotting disorders like factor V Leiden. At Penn Medicine, our specialists review your personal and family history, offer advanced testing, including genetic testing services when appropriate, and build a care plan to help lower your risk of blood clots.

Factor V Leiden is classified by whether you inherit the mutation from one parent or both parents. Knowing which type you have helps your care team better understand your risk for developing blood clots.

There are two types:

• One copy of the mutation (heterozygous): This is the most common form. Most people never develop a blood clot, although the risk is higher than in people without the mutation.
• Two copies of the mutation (homozygous): This less common form is inherited from both parents and carries a greater risk of developing blood clots. Your care team may recommend additional preventive measures during higher-risk situations.

Factor V Leiden is caused by an inherited change in the gene that makes clotting factor V. Because the mutation is passed from biological parents to their children, it can run in families.

If you’re diagnosed, it’s worth talking with close biological relatives about testing, since knowing their status early can help them make informed choices about their own health.

A blood test can confirm whether you have factor V Leiden. Your provider may recommend testing if you’ve had one or more blood clots, especially at a younger age than expected, or if a close biological family member has a history of blood clots.

There are two main tests used to diagnose the condition. Your provider may start with an activated protein C (APC) resistance assay, a blood test that checks how your blood responds to a natural anticoagulant protein. If this test shows resistance, it strongly suggests factor V Leiden. From there, genetic testing looks directly at your DNA to confirm the exact mutation and is the most definitive way to diagnose the condition.

Factor V Leiden is a lifelong genetic condition, but many people never need treatment. Care focuses on preventing blood clots and treating them if they occur. Your provider may still recommend extra precautions during times when your clotting risk is higher, like surgery, long periods of bed rest, or pregnancy.

If you’ve had a blood clot, your provider may recommend:

• Anticoagulant medication (blood thinners): Medicines that treat existing blood clots and help prevent new ones.
• Compression stockings: These put gentle pressure on your legs to improve blood flow and lower your risk of a clot.
• Walking soon after surgery: Moving around as soon as it’s safe can help lower your risk of a clot forming.

When you’re diagnosed with factor V Leiden, you want a care team that treats blood clotting disorders every day. Penn Medicine’s hematologists have extensive experience diagnosing and treating clotting conditions, and they work closely with other specialists to help prevent serious complications related to blood clots.

If you’re pregnant or taking hormone therapy, our specialists offer added expertise for these higher-risk situations. And because clotting risk can change quickly, our team also helped develop testing that measures the levels of newer blood thinners in your system, so your care team can act fast when it matters most.