Factor V Leiden is a mutation of one of the clotting factors in the blood known as factor V. The mutation may increase the risk of developing abnormal blood clots (thrombophilia) in the veins.

Most people with factor V Leiden never develop abnormal clots; however, those that do develop clots may face long-term health problems that may even become life threatening.

Factor V Leiden mutation can develop in both men and women. Women may have a slightly greater tendency for blood clots during pregnancy or when taking the hormone estrogen.

Anticoagulant medications are used to treat factor V Leiden that produces blood clots and they can lessen the risk of developing additional blood clots in order to avoid serious complications.



The first indication of the disorder may be the development of a blood clot (thrombosis). Some clots do no damage and disappear on their own. Others may be life threatening. Symptoms of a blood clot depend on where it forms and whether and where it travels.


A clot in a deep vein


Known as deep vein thrombosis (DVT), this condition may be asymptomatic, but if symptoms do occur, they most commonly affect the legs (swelling of the ankles and feet). Other symptoms include:


  • Pain
  • Significant swelling
  • Redness
  • Warmth


A clot closer to the surface of the skin


This is known as superficial venous thrombosis, phlebitis or thrombophlebitis. Symptoms usually include:


  • Warmth
  • Redness
  • Tenderness or pain (in or around the vein with the blood clot)


A clot that travels to the lungs


A clot that travels to the lungs is called a pulmonary embolism. This occurs when a deep vein clot breaks off a travels through the right side of the heart to the lung where it obstructs blood flow. This can be a life-threatening emergency. Symptoms may include:


  • Sudden shortness of breath
  • Chest pain when breathing in
  • A cough that produces bloody or blood-streaked sputum
  • Rapid heart rate (tachycardia)



A blood clot (thrombus) normally forms to stop the bleeding when an artery or vein is damaged, such as from a cut or an injury. Clots are formed by chemical reactions between certain blood cells (platelets) and proteins in the blood (clotting factors). Anti-clotting factors prevent an excessive formation of blood clots.

Normally, factor V is a clotting protein. Anti-clotting proteins break up factor V to keep it from forming clots when it is not necessary.

Factor V Leiden mutation makes it difficult for anti-clotting proteins to break up factor V. This prolongs factor V’s presence in the blood and increases the risk of clotting.

Factor V Leiden is an inherited disorder in which one inherits either one copy (heterozygous) or rarely two copies (homozygous) of the defective gene. Inheriting two copies of the gene (one from each parent) significantly increases the risk of developing blood clots.


Risk factors

A family history of factor V Leiden increases the risk of inheriting the disorder. The condition is most common in people who are white and of European descent.



Complications associated with factor V Leiden include:


  • Pregnancy complications: the disorder has been associated with an increased risk of miscarriage and other complications during pregnancy including pregnancy-induced high blood pressure (preeclampsia), slow fetal growth and early separation of the placenta from the uterine wall (placental abruption).
  • Deep vein thrombosis (DVT): the disorder increases the risk of developing DVT compared to people without the mutation.
  • Pulmonary embolism: DVT increases the risk of a clot breaking off and travelling to the lungs or in rare cases, the brain. A pulmonary embolism can be fatal. It is crucial to acquire emergency medical attention when symptoms of a pulmonary embolism occur.