What Is DVT?

DVT goes by a number of names:

• Deep-vein thrombosis (throm-BO-sis)
• Deep venous thrombosis
• Venous thromboembolism (VTE)
• Blood clot in the legs
• Venous thrombosis
• The "silent killer"

DVT occurs when a blood clot forms in one of the body's large veins blocking the blood flow. Typical symptoms include pain, swelling, redness and enlarged surface veins. Called "the silent killer," DVT can also have no symptoms.⁶ Only about half of the people with DVT have symptoms.⁷

As a result of effective public education, many people understand a clot in an artery may lead to a heart attack or stroke. DVT is a different disease and does not occur in arteries, only in the large blood vessels that are enclosed by muscle and located in the center of an arm or leg or lower body. DVT is most common in the leg (calf or thigh).

If left untreated, a blood clot partially or completely blocking blood flow, could completely dissolve over time without any lingering problems or could break off and travel through the blood stream to the lungs. This traveling clot, which is called an embolism, and any embolism that lodges in the pulmonary circulatory system is called a pulmonary embolism (PE). A pulmonary embolism can lead to death. The larger the DVT clot, the greater the risk of developing pulmonary embolism. The larger the DVT clot, the greater the risk of developing a pulmonary embolism. Deep-vein clots in the upper leg are more serious than those in the lower leg because those in the thigh are more likely to travel to the lung.

Deep vein clots are much more dangerous than a bruise or a clot just beneath the skin. A clot in the deep veins is more likely to break off and travel through the vein from the leg or pelvic area and then lodge in an artery of the lung. An estimated 30 percent of people with venous thromboembolism (VTE) die within 30 days, one-fifth suffers sudden death due to a clot in the lungs, and about 30 percent develop recurrent VTE within 10 years.⁸ Of those who die, many do so within 30 to 60 minutes after symptoms begin.⁹ Nine out of 10 cases of pulmonary embolism are caused by blood clots that form in the legs and then travel to the lungs. Yet, with immediate diagnosis and treatment, most DVTs do not become life threatening.

Blood clots can result from immobility, such as:

• Bed rest or travel
• Recent surgery or injury, especially involving the lower body
• Broken bones
• Use of hormones such as birth control pills or estrogen

Since most blood clots form in the legs, think about the sitting position. Sitting requires bending the knees. Maintaining this bent-knee position for a long period of time puts pressure and squeezes the vein located behind the knee, which can lead to a blood clot. In this case, the blood clotting is mechanical, interfering with the flow of blood.

The other way blood clots form is chemical. The chemistry of the blood can cause a slow or sluggish flow of blood or cause the blood to clot too quickly. The use of hormones might have an effect on the make-up of the blood.

⁶ Anderson, F.A., and Audet, A.M. (1998) “Best Practices Preventing Deep Vein Thrombosis and Pulmonary Embolism.” University of Massachusetts Medical School, Center for Outcomes Research. Available on the World Wide Web: www.outcomes-umassmed.org/dvt/.

⁷ Ibid.

⁸ American Heart Association Statistics Committee and Stroke Statistics Subcommittee (Jan. 12, 2006) “Heart Disease and Stroke Statistics: 2006 Update.” Circulation 113:e85-151e. Available on the World Wide Web: http://circ.ahajournals.org/cgi/content/full/113/6/e85.

⁹ Bren, L. (Nov.-Dec. 2004) “Avoid Deep Vein Thrombosis: Keep the Blood Flowing.” FDA Consumer Magazine. Available on the World Wide Web: www.fda.gov/fdac/features/2004/604_vein.html.