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Factor V Leiden


Disease: Factor V Leiden Factor V Leiden
Category: Blood diseases & tumors
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Disease Definition:

In a common inherited genetic disorder called factor V Leiden, the blood has an increased tendency to form clots (thrombophilia), usually in the veins.


Blood clots could form at any age, but usually, the risk of clotting in most people does not begin until adulthood. Usually, people with factor V Leiden do not develop abnormal clots, but they do develop clots that cause long-term health problems or clots that are life-threatening.


Even though women have an increased risk of developing blood clots when taking the hormone estrogen or during pregnancy, but both women and men can have factor V Leiden.


In case someone has factor V Leiden, they should take medications to avoid potentially serious complications and to lessen the risk of developing blood clots.

Work Group:

Prepared by: Scientific Section

Symptoms, Causes


Sometimes, a person may have factor V Leiden without developing any signs or symptoms. However, the development of a blood clot (thrombosis) could be the first indication of this disorder.


Although some clots could disappear without inflicting any damage, but others could be life-threatening. Usually, clots could form either in the arteries or veins; however, they are much more likely to develop in the veins in case the person factor V Leiden.


The signs and symptoms that occur in the case of a venous clot will depend on where it forms, whether it travels and where:


A clot that forms closer to the surface of the skin:

Known as phlebitis, thrombophlebitis or superficial venous thrombosis, its signs and symptoms include pain, redness in the affected area, tenderness and warmth.


A clot that develops in a deep vein:

Known as DVT (deep vein thrombosis), its signs and symptoms include redness, warmth in the affected limbs, usually the legs, including the ankles and feet, in addition to significant swelling and pain.


A clot that travels to the lungs:

This occurs when a deep vein clot breaks free and travels through the right side of the heart to the lungs and blocks blood flow. Known as pulmonary embolism, its signs and symptoms include a cough that produces bloody or blood-streaked sputum and rapid heartbeat (tachycardia), chest pain when breathing in and sudden shortness of breath.


The doctor should be contacted in case the patient:


  • Develops signs and symptoms of DVT, including leg pain and swelling.
  • Has had one or more blood-clotting incidents without an apparent reason.
  • Has family members who have factor V Leiden or the family has a history of blood clots. The patient should also ask the doctor about the risks and benefits of genetic testing for this disorder.


Medical attention should be immediately sought in case someone develops signs and symptoms of a pulmonary embolism, including chest pain or discomfort.


When an artery or vein is damaged, usually a blood clot (thrombus) forms in order to stop bleeding, such as when someone experiences a cut. As a result of chemical reactions between specialized blood cells called platelets and proteins in the blood (clotting factors), blood clots occur. Excessive formation of blood clots is controlled by anti-clotting factors. Factor V is one of the clotting proteins. When people have factor V Leiden, it means that their factor V protein responds more slowly to the anti-clotting factors due to a genetic mutation.


Normally, in the clotting process, anti-clotting proteins combine in order to help break up factor V and keep it from being reused and forming clots when clotting isn’t needed. But in case someone has factor V Leiden, this mutation will not allow the anti-clotting proteins to break down factor V, keeping it in the blood longer and increasing the chance of clotting.


Factor V Leiden could be inherited from one parent, which is when someone inherits only one copy of the defective gene (heterozygous), slightly increasing their risk of developing blood clots. Or someone could inherit two copies of the defective gene, one from each parent (homozygous), significantly increasing their risk of developing blood clots.



A variety of serious or potentially serious complications could be caused by the abnormal blood clotting of factor V Leiden, such as:


DVT (deep vein thrombosis):

When a complication of a deep vein clot occurs, it could damage the valves in the veins of the affected leg which normally serve to keep the blood flowing upward to the heart. This damage could cause a condition called chronic venous insufficiency, which in turn causes chronic swelling and discoloration in the lower leg due to the impaired flow of blood.


Complications during pregnancy:

The mutation in factor V Leiden has been linked with an increased risk of miscarriage and the possibility of other complications during pregnancy, such as slow fetal growth, early separation of the placenta from the uterine wall (placental abruption) and pregnancy-induced high blood pressure (preeclampsia). However, most women with factor V Leiden have normal pregnancies. A woman should be carefully monitored throughout her pregnancy in case she has factor V Leiden.


Pulmonary embolism:

A person will be at risk of a clot breaking off and traveling to the lungs, or in some rare cases, the brain, because of a DVT. It is vital to watch for signs and symptoms of a pulmonary embolism and to seek prompt medical attention, because a pulmonary embolism could be fatal.


When treating people who develop blood clots, the medications that are used include anticoagulant (blood thinning) medications, such as heparin, low molecular weight heparin or warfarin .


In case someone hasn't had any blood clots when being tested because of a family history of factor V Leiden, they probably won’t be prescribed anticoagulants unless they're in a high-risk situation, such as being hospitalized for surgery or other medical reasons. In these cases, they might receive preventive doses of anticoagulants during the hospital stay.


A combination of heparin and warfarin will be the standard initial treatment for someone who has a thrombosis. After the initial treatment, the heparin will be discontinued and the warfarin continued. The condition of thrombosis will determine how long someone needs to take the medication.


Heparin is an anticoagulant medication that works quicker than warfarin, however, until recently, it had to be monitored closely and administered intraveniously. Dalteparin , and enoxaparin are the newer forms of heparin, which are known as low molecular weight heparin that the patient can inject him/herself. This drug is considered safe to take during pregnancy.


Warfarin is yet another anticoagulant medication that is easier to take than heparin because it comes in pill form. Warfarin usually isn’t recommended during pregnancy, particularly in the first trimester because in some rare cases it could cause birth defects. However, warfarin could be prescribed after the first trimester in case its benefits outweigh its risks.



During pregnancy, anticoagulant therapy is particularly complex. This therapy carries some significant risks of side effects and is quite expensive.



In order to be sure that the patient's blood is capable of clotting enough to stop bleeding in case they bruise or cut themselves, blood tests will be done to monitor the dosage of the anticoagulant.


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