What is Deep vein thrombosis?

Deep vein thrombosis

What is deep vein thrombosis?

If you have deep vein thrombosis (DVT for short), it means a blood clot has formed in one of your deep veins, probably one going through the muscles of one of your legs.

Veins are blood vessels that carry blood back to your heart from all over your body. If a vein in your leg gets partly or completely blocked by a blood clot, your leg can become swollen and painful.

You can get a clot below the knee (this is called calf DVT), or above the knee (this is called proximal DVT).

If part of the blood clot in your leg breaks off, it can go back through your heart and get stuck in an

arteries
Arteries are the blood vessels that take blood that is rich in oxygen and food away from your heart. The arteries carry this blood to all the tissues in your body.

artery in one of your lungs. This is called a

pulmonary embolism
A pulmonary embolism can give you chest pain, make you feel breathless and uncomfortable or make you breathe rapidly. A pulmonary embolism is dangerous and can kill you if it is not treated.

pulmonary embolism, and it can be dangerous. Pulmonary embolism is more likely to happen if the clot is above your knee than if it's below your knee. So a clot above the knee is more serious.

Source:
Hull RD, Pineo GF.
Prophylaxis of deep venous thrombosis and pulmonary embolism: current recommendations.
Medical Clinics of North America. 1998; 82: 477-493.

Source:
Baker WF Jr.
Diagnosis of deep venous thrombosis and pulmonary embolism.
Medical Clinics of North America. 1998; 82: 459-476.

Normally, your blood forms clots to stop the bleeding if you injure yourself. But clots can also form inside your blood vessels. Some people are more likely to get clots in a vein in their leg than others. You're more likely to get DVT if you are:

Source:
American Public Health Association.
Deep vein thrombosis: advancing awareness to protect patient lives.
February 2003. White paper from the Public Health Leadership Conference on Deep-Vein Thrombosis. Available at http://www.apha.org (accessed on 15 December 2008).

Source:
Hirsh J, Hoak J.
Management of deep vein thrombosis and pulmonary embolism.
Circulation. 1996; 93: 2212-2245.

⁴

Source:
British Thoracic Society.
British Thoracic Society guidelines for the management of suspected acute pulmonary embolism.
Thorax. 2003; 58: 470-484.

⁵

Source:
Huerta C, Johansson S, Wallander MA, et al.
Risk factors and short-term mortality of venous thromboembolism diagnosed in the primary care setting in the United Kingdom.
Archives of Internal Medicine. 2007; 14: 935-943.

⁶

Older
Overweight.

You are also more likely to get DVT if you:

Source:
Hirsh J, Hoak J.
Management of deep vein thrombosis and pulmonary embolism.
Circulation. 1996; 93: 2212-2245.

⁴

Source:
British Thoracic Society.
British Thoracic Society guidelines for the management of suspected acute pulmonary embolism.
Thorax. 2003; 58: 470-484.

⁵

⁶

Have cancer
Have had DVT before
Have recently had a fracture
Have varicose veins
Have inflammatory bowel disease (conditions that cause

inflammation
If your skin or some other part of your body becomes red, swollen, hot or sore, we say it is inflamed. It means that your body is trying to protect you from germs, from something in your body tissues that can hurt you (like a thorn or sliver), or from things that cause allergies (allergens). Inflammation is part of the way the body heals an infection or injury.

inflammation of your bowel, such as

Crohn's disease
Crohn's disease causes iflammation in your bowel. It usually affects your small intestine, but can happen anywhere in your digestive tract. It causes diarrhea and bloody stools.

Crohn's disease and

ulcerative colitis
Ulcerative colitis is a disease that affects the wall of your large intestine. Ulcerative colitis causes you to have diarrhea and get blood in your stools. Ulcerative colitis is an autoimmune disease. This means that you get it when your body attacks part of itself.

ulcerative colitis)
Take

steroids
Steroids are a type of chemical. Your body naturally produces steroids, which play a part in many of its processes. For example, steroids are involved in how your immune system, reproductive system and metabolism work. Steroids can also be given as medicines and are used for a number of different conditions: including asthma, rheumatoid arthritis and eczema. Corticosteroids are not the same as the steroids used by some body builders and athletes. Those steroids are called 'anabolic steroids'.

steroid pills regularly
Sit or lie for long periods without moving much
Have an operation, especially on your leg
Have a problem with blood clotting (these problems can run in families).

If you are a woman, your chance of getting DVT is higher if you are:

Pregnant
Taking birth control pills or

hormone replacement therapy
Hormone replacement therapy (also called HRT) is given to women after menopause to replace the estrogen (the main female hormone) that is no longer made by their ovaries. It can be given either as estrogen alone or as a combination of estrogen and progestin (another female hormone). It is useful to treat menopausal symptoms such as hot flushes, and to prevent brittle bone disease (osteoporosis). But there are concerns that it may increase the risk of breast cancer, heart attacks and strokes.

hormone replacement therapy (HRT).

Some research has found that long-distance travel increases your chance of having DVT. For example, one study suggested that, during long-distance flights, about 1 in 10 passengers older than 50 are at risk of getting DVT without any symptoms.

Source:
Scurr JH, Machin SJ, Bailey-King S, et al.
Frequency and prevention of symptomless deep venous thrombosis in long-haul flights: a randomised trial.
Lancet. 2001; 357: 1485-1489.

⁷ A more recent study suggested that 1 in 100 people traveling long distances by air may get symptoms of a blood clot.

Source:
Hughes R, Hopkins R, Hill S, et al.
Frequency of venous thromboembolism in low to moderate risk long distance air travellers: the New Zealand Air Traveller's Thrombosis (NZATT) study.
Lancet. 2003; 362: 2039-2044.

⁸ To learn more about the symptoms, see What are the symptoms of deep vein thrombosis?

The higher risk could be because, during long-distance journeys, people are sitting still and not doing any exercise for long periods. But doctors aren't quite sure. It may be that people who get DVT while traveling long distances are at risk for other reasons.

If you have a long journey to make, you can do things that might lower your risk of getting DVT. To learn more, see Long-distance travel and DVT.

Sources for the information on this page:

Hull RD, Pineo GF.Prophylaxis of deep venous thrombosis and pulmonary embolism: current recommendations.Medical Clinics of North America. 1998; 82: 477-493.

Baker WF Jr.Diagnosis of deep venous thrombosis and pulmonary embolism.Medical Clinics of North America. 1998; 82: 459-476.

American Public Health Association.Deep vein thrombosis: advancing awareness to protect patient lives.February 2003. White paper from the Public Health Leadership Conference on Deep-Vein Thrombosis. Available at http://www.apha.org (accessed on 15 December 2008).

Hirsh J, Hoak J.Management of deep vein thrombosis and pulmonary embolism.Circulation. 1996; 93: 2212-2245.

British Thoracic Society.British Thoracic Society guidelines for the management of suspected acute pulmonary embolism.Thorax. 2003; 58: 470-484.

Huerta C, Johansson S, Wallander MA, et al.Risk factors and short-term mortality of venous thromboembolism diagnosed in the primary care setting in the United Kingdom.Archives of Internal Medicine. 2007; 14: 935-943.

Scurr JH, Machin SJ, Bailey-King S, et al.Frequency and prevention of symptomless deep venous thrombosis in long-haul flights: a randomised trial.Lancet. 2001; 357: 1485-1489.

Hughes R, Hopkins R, Hill S, et al.Frequency of venous thromboembolism in low to moderate risk long distance air travellers: the New Zealand Air Traveller's Thrombosis (NZATT) study.Lancet. 2003; 362: 2039-2044.

This information was last updated on Jan 09, 2009

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment.
© BMJ Publishing Group Limited 2009. All rights reserved.

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