Deep venous thrombosis (DVT) mainly affects the large veins in the lower leg and thigh. The clot can block blood flow. If the clot breaks off and moves through the bloodstream, it can get stuck in the brain, lungs, heart, or other area, leading to severe damage.

Risks for DVT include:

• Sitting for a long time, such as on a long plane or car trip
• Bedrest
• Recent surgery (especially hip, knee, or female reproductive organ surgery)
• Fractures
• Giving birth within the last 6 months
• Medications such as estrogen and birth control pills
• Cigarette smoking
• Obesity

You're also more likely to develop DVT if you have any of the following conditions:

• Overproduction of red blood cells in bone marrow (polycythemia vera )
• Cancerous tumors
• Blood that more likely to clot (hypercoagulability)

DVTs are most common in adults over age 60, but can occur at any age.

• Leg pain in one leg
• Leg tenderness in one leg
• Swelling (edema) of one leg
• Increased warmth in one leg
• Changes in skin color (redness) in one leg

Your health care provider will perform a physical exam. The exam may show a red, swollen, or tender leg.

The following tests may be done:

• X-rays to show veins in the legs (leg venography )
• Doppler ultrasound exam of a limb
• Plethysmography of the legs
• D-dimer blood test

Blood tests may be done to check for increased blood clotting. Such tests include:

• Antithrombin III
• Genetic testing to look for mutations that make you more likely to develop blood clots, including factor V Leiden and prothrombing 20210a
• DIC screening
• Lupus anticoagulant

This list is not all-inclusive.

For years, the standard treatment has been a medication called heparin, which stops blood clots from forming. This type of medicine is called an anticoagulant.

If heparin is given continuously through a vein (IV), you must stay in the hospital. However, newer forms of heparin that can be given by injection once or twice a day can sometimes be used. Usually, it's a drug called enoxaparin. You may not need to stay in the hospital as long, or at all, if you are prescribed this newer form of heparin.

The drug warfarin may be prescribed in combination with heparin. Warfarin is taken by mouth. It usually takes several days to fully work. Heparin is continued until the warfarin has been fully effective for at least 24 hours. People will take warfarin for about 6 months, depending on their risk for another clot.

You will need frequent lab tests when you first start taking warfarin to check the thickness of your blood, so your health care provider can properly adjust your dose.

In rare cases, surgery may be needed if medicines do not work. Surgery may involve:

• Removal of a large blood clot from the vein or injection of clot-busting medicines
• Placement of a screen in the body's largest vein to prevent blood clots from traveling to the lungs

Many DVT's disappear without a problem, but they can return. Some people may have long-term pain and swelling in the leg known as post-phlebitic syndrome. Wearing tight (compression) stockings may help relieve this problem.

A blood clot that breaks free in the leg and travel to the lungs (pulmonary embolus ) can be life threatening. Rapid treatment of DVT helps prevent this problem.

Call your health care provider if you have DVT-like symptoms.

Go to the emergency room or call the local emergency number (such as 911) if you have DVT and you develop chest pain , difficulty breathing , fainting , loss of consciousness , or other severe symptoms.

Doctors may prescribe blood thinners to help prevent DVT in high-risk people or those who are undergoing high-risk surgery.

Sometimes patients in the hospital wear special soft boots that automatically (and gently) squeeze the calves every now and then. This is called intermittent pneumatic compression. It helps keep blood moving and prevents blood clotting.

Moving your legs often during long plane trips, car trips, and other situations in which you are sitting or lying down for long periods of time can also help prevent DVT.

Brotman DJ, Jaffer AK. Prevention of venous thromboembolism in the geriatric patient.Cardiol Clin. 2008 May;26(2):221-34, vi.