venous thromboembolism

introduction

The term venous thromboembolism (VTE) is used to collectively describe deep vein thrombosis and pulmonary embolism.

When a blood clot (thrombus) forms inside a person´s vein, he or she is said to suffer from venous thrombosis. If the vein affected by a blood clot is deep inside the body, rather than close to the surface of the body, the condition is referred to as deep vein thrombosis (DVT) and most often occurs in the veins of the legs or pelvis.

Patients with DVT are in danger of suffering a pulmonary embolism, which occurs when a venous blood clot breaks off (completely or partially), travels with the bloodstream and lodges in one of lung´s narrow arteries. The resulting blockage of blood flow can cause permanent damage to the affected lung, heart failure and death.

Individuals who suffer from either DVT or pulmonary embolism are collectively diagnosed as having venous thromboembolism (VTE). Each year, one out of 1000 individuals of European ancestry in the United States is diagnosed for the first time with VTE. About one-third of people with this condition experience a pulmonary embolism and one-third develops VTE again within ten years of the initial diagnosis. The proportion of people with VTE is likely to be underestimated as it is well recognized that a number of cases remain undiagnosed.

It is believed that a number of genetic factors contribute to the development of VTE. One of these is Factor V Leiden, a mutation in the Factor V gene on chromosome 1 that results in thrombophilia, or an increased tendency to form abnormal blood clots in blood vessels. Individuals with this mutation have a three to four-fold increased risk of developing VTE in their lifetime. The Factor V Leiden variant is quite common in populations of European ancestry, but less common in other ethnicity groups.

The deCODEme Genetic Scan identifies the Factor V Leiden variant in the Factor V gene and provides interpretation of the associated risk of development of VTE for individuals of European ancestry. Currently, information about the risk of VTE conferred by this genetic variant is not available for individuals of other ethnicities.

risk factors

• Age and gender: Age is a strong risk factor for development of venous thromboembolism (VTE) with a dramatic increase after age 60. Recurrent VTE is more common in men than women.
• Surgeries: Major surgery, as well as trauma and fractures, are known to increase the risk of VTE.
• Chronic illnesses: Increased risk of VTE accompanies various chronic illnesses such as cancer, stroke and congestive heart failure. A previous diagnosis of VTE is a risk factor for further episodes.
• Immobility: Immobility associated with surgeries, trauma and chronic illnesses is associated with VTE as described above. Prolonged bed rest and long journeys by airplane or car, even in otherwise assumed healthy individuals, also increase the risk of VTE.
• Other: Other conditions that have been associated with greater risk of VTE include pregnancy, the postpartum period, varicose veins, obesity, estrogen treatment and the antiphospholipid antibody syndrome.
• Ethnicity: In the United States the incidence of VTE has been found to be highest in African-Americans followed by individuals of European descent. The risk for Hispanics is about half that of populations of European origin while Asians are at a markedly lower risk.
• Genetics: An inherited risk factor can be identified in over half of patients with deep venous thrombosis without identifiable cause or thrombosis at a young age. Factor V Leiden, is detected in about 5% of individuals of European origin, but is rare in other ethnic groups. The reported frequency in Hispanics is around 2%, 1% in African-Americans and 0.5% or less in Asians.

more information

You can find out more information about VTE by talking with your doctor and visiting these Web sites:
• American Heart Association article on Pulmonary Embolism and Deep Vein Thrombosis
• About Factor V Leiden by the Thrombophilia Awareness Project JAMA patient page on Deep Vein Thrombosis
• National Heart Lung and Blood Institute (NHLBI) article on Deep Vein Thrombosis
• Medline Plus article on Deep Vein Thrombosis
• Society of Interventional Radiology on Deep Vein Thrombosis

scientific references

1. Anderson FA Jr, Spencer FA. Risk factors for venous thromboembolism. Circulation. 2003 Jun 17;107(23 Suppl 1):I9-16.
2. White RH. The epidemiology of venous thromboembolism. Circulation. 2003 Jun 17;107(23 Suppl 1):I4-8.
3. Ridker PM, Miletich JP, Hennekens CH, Buring JE. Ethnic distribution of factor V Leiden in 4047 men and women. Implications for venous thromboembolism screening. JAMA. 1997 Apr 23-30;277(16):1305-7.
4. Lee R. Factor V Leiden: a clinical review. Am J Med Sci. 2001 Aug;322(2):88-102.