Deep venous thrombosis is a condition in which a blood clot forms in a vein that is deep inside the body.

Causes

Deep venous thrombosis (DVT) mainly affects the large veins in the lower leg and thigh. The clot can block blood flow and cause swelling and pain. When a clot breaks off and moves through the bloodstream, this is called an embolism. An embolism can get stuck in the brain, lungs, heart, or other area, leading to severe damage.

Blood clots may form when something slows or changes the flow of blood in the veins. Risk factors include:

• After a pacemaker catheter has been passed through the vein in the groin
• Bedrest
• Cigarette smoking
• Fractures in the pelvis or legs
• Giving birth within the last 6 months
• Heart failure
• Medications such as estrogen and birth control pills
• Obesity
• Recent surgery (especially hip, knee, or female reproductive organ surgery)
• Too many blood cells being made by the bone marrow (polycythemia vera), causing the blood to be thicker and slower than normal

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

• Blood that is more likely to clot (hypercoagulability)
• Cancer
• Taking estrogens or birth control pills. This risk is even higher if you smoke.

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

Sitting for long periods when traveling can increase the risk of DVTs. This is most likely when one or more of the risk factors listed above are also present.

Symptoms

• Changes in skin color (redness) in one leg
• Increased warmth in one leg
• Leg pain in one leg (it may hurt to place all of your weight on this leg when standing)
• Leg tenderness in one leg
• Skin that feels warm to the touch
• Swelling (edema) of one leg

Exams and Tests

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:

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

Blood tests may be done to check if there is increased chance of blood clotting (hypercoagulability). Such tests include:

• Activated protein C resistance (checks for the Factor V Leiden mutation)
• Antithrombin III levels
• Genetic testing to look for mutations that make you more likely to develop blood clots, including the prothrombin G20210A mutation
• Lupus anticoagulant or antiphospholipid antibodies
• Protein C and protein S levels
• Screening for disseminated intravascular coagulation (DIC)

This list is not all-inclusive.

Treatment

Your doctor will give you medicine to thin your blood (called an anticoagulant). This will keep more clots from forming or old ones from getting bigger. These drugs cannot dissolve existing clots.

Heparin is usually the first drug given.

• If heparin is given through a vein (IV), you must stay in the hospital.
• Newer forms of heparin can be given by injection once or twice a day. You may not need to stay in the hospital as long, or at all, if you are prescribed this newer form of heparin.

A drug called warfarin (Coumadin) will be started along with heparin. Warfarin is taken by mouth. It takes several days to fully work. Heparin is not stopped until the warfarin has been at the right dose for at least 24 hours. You will most likely take warfarin at least 3 months. Some people must take it for the rest of their lives, depending on their risk for another clot.

When you are taking warfarin, you may be more likely to bleed, even from activities you have always done.

Changing how you take your warfarin, taking other medicines, and eating certain foods all can change the way the warfarin works in your body. If this happens, you may be more likely to form a clot or have bleeding problems.

• Take the medicine just the way your doctor prescribed it
• Know what to do if you miss a dose
• You will need to get blood tests often to make sure you are taking the right dose

You will be given pressure stocking prescribed by your doctor. They will improve blood flow in your legs, and reduce your risk for blood clots. It is important to wear these every day.

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

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

Outlook (Prognosis)

Many DVTs 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 during and after the DVT may help prevent this problem.

Blood clots in the thigh are more likely to break off and cause pulmonary embolism (PE) than blood clots in the lower leg or other parts of the body.

Possible Complications

A blood clot can break free in the leg and travel to the lungs (pulmonary embolus) or anywhere else in the body, and can be life threatening. Rapid treatment of DVT helps prevent this problem.

Post-phlebitic syndrome refers to long-term swelling (edema) in the leg that had the deep vein thrombosis. Changes in skin color and pain can also be present. These symptoms may be noticed right away, or may not develop for one or more years afterward. This problem is called post-thrombotic syndrome.

When to Contact a Medical Professional

Call your health care provider if you have symptoms of DVT.

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, coughing blood, fainting, loss of consciousness, or other severe symptoms.

Prevention

Wear the pressure stockings your doctor prescribed. They will improve blood flow in your legs and reduce your risk for blood clots.

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

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. People at very high risk for blood clots may need heparin shots when they are on a flight that lasts longer than 4 hours.

Do not smoke. If you smoke, quit. Women who are taking estrogen must stop smoking. See: Smoking - tips on how to quit.

Alternative Names

DVT; Blood clot in the legs; Thromboembolism; Post-phlebitic syndrome; Post-thrombotic syndrome