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What is Factor V Leiden?

The most common genetic risk factor for venous thrombosis is factor V Leiden, present in 5 percent of the general population. Factor V is one of the normal blood clotting factors. Factor V Leiden is a changed or ‘mutated’ form of factor V which is inactivated ten times slower that the normal factor V. This causes it to persist longer in the circulation, resulting in a hypercoagulable state. In other words, the blood continues clotting, resulting in possible obstruction.

One copy of the Factor V Leiden gene increases the risk for venous thrombosis 4 to 8 times, while two copies of the gene increase the risk 80-fold.

Other coexisting coagulation defects can occur with Factor V Leiden, and in general, the risk for thrombosis increases in patients with more than one genetic defect.

The factor V Leiden mutation is involved in 20 to 40 percent of venous thrombosis cases and is suspected in individuals who have a medical history of venous thrombosis or in families with a high incidence of venous thrombosis.

What is thrombosis?

Thrombosis occurs when clots obstruct veins (blood vessels that carry blood from the body back into the heart) or arteries (blood vessels that carry oxygenated blood away from the heart to the body). Venous thrombosis is when the blood clot obstructs a vein, and arterial thrombosis is when the blood clot obstructs an artery.

What causes thrombosis?

Venous thrombosis may be the result of the following:

  • disease or injury to the veins in the legs
  • immobility for any reason
  • fracture
  • certain medications
  • obesity
  • inherited disorders or inherited predisposition

Pooling (stasis) of blood in the legs and subsequent clotting can result in varicose veins. Clots in the legs may break loose and travel to the lungs, causing pulmonary clots that can result in respiratory distress, pain, and in extreme cases, death.

Arterial thrombosis may be the result of arteriosclerosis (hardening of the arteries where fatty or calcium deposits cause the arterial walls to thicken) of blood vessels (clots form on abnormal blood vessel surfaces).

When arterial thrombosis occurs in the coronary arteries (the two arteries that come from the aorta to provide blood to the heart muscle), it can lead to heart attacks. When it occurs in the cerebral (brain) circulation, it can lead to strokes or lack of oxygen to other organs.

What are the symptoms of thrombosis?

The following are the most common symptoms of thrombosis. However, each individual may experience symptoms differently. Symptoms may include:

  • increased blood clots in arteries and veins
  • pain isolated to one leg (usually the calf or medial thigh)
  • swelling in the extremity
  • varicose veins

The symptoms of thrombosis may resemble other blood disorders or medical problems. Always consult your physician for a diagnosis.

How is thrombosis diagnosed?

In addition to a complete medical history and physical examination, diagnostic procedures for thrombosis may include additional blood tests including hypercoagulability panels. Dye injection and catheterization is also used to diagnose the presence of arterial and venous thrombosis.

Treatment for thrombosis:

Specific treatment for thrombosis will be determined by your physician based on:

  • your age, overall health, and medical history
  • extent and type of thrombosis
  • your tolerance for specific medications, procedures, or therapies
  • expectations for the course of the disease
  • your opinion or preference

Treatment may include:

  • anticoagulant medications, such as coumadin and heparin
  • catheters (to expand the width, or lumen, of involved vessels)
  • medications, such as tissue plasminogen activator (t-PA) and/or enzymes, such as streptokinase (to dissolve clots)

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Online Resources of Hematology & Blood Disorders

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