Deep Vein Thrombosis

Deep vein thrombosis, or DVT, is a blood clot that forms in a vein deep in the body. These blood clots can cause pain and swelling, though there may be no symptoms. They can also break off and travel to the lungs. Most deep vein blood clots occur in the lower leg or thigh, but they also can occur in other parts of the body.

When a DVT breaks off and travels through the bloodstream, it becomes lodged in a blood vessel. This loose clot is called an embolus. The danger is that an embolus may cause blockage of that vessel. When the embolus travels to the lungs and blocks blood flow, the condition is called a pulmonary embolism, or PE. Pulmonary embolism is a very serious condition. It can damage the lungs and other organs in the body and become life-threatening.

Pulmonary embolism is more likely to form from blood clots traveling from the thigh than from clots traveling from the lower leg or other parts of the body.

Three factors lead to DVTs. The first is the slowing of blood flow, a process called venous stasis. The second is injury to the vein. The last is an inherent tendency to form clots, which some people have more strongly than others.

Blood clots can also form in the superficial veins, or the veins close to the surface of the skin. However, these clots are not considered DVTs and will not cause PE.

Other Names

• Blood clot
• Venous thrombosis
• Deep venous thrombosis
• Venous thromboembolism (VTE), a term used for both deep vein thrombosis and pulmonary embolism

Signs and Symptoms

Symptoms of DVT may occur before the clot travels to the lungs, or after PE. Both DVT and PE can cause serious, possibly life-threatening complications if not treated.

Deep vein thrombosis

Only about half of people with DVT have symptoms. These symptoms occur in the leg affected by the clot and include the following:

• Swelling of the leg or along a vein
• Pain or tenderness, which may only be felt while standing or walking
• Increased warmth in the area that is swollen or in pain
• Red or discolored skin

Pulmonary embolism

Some people don't know they have DVT until they have signs or symptoms of PE. Below are some symptoms of PE:

• Shortness of breath or rapid breathing
• Fast heart rate
• Pain with deep breathing
• Coughing up blood

Rapid breathing and a fast heart rate are the most common signs of PE, but it can be subtle or can mimic other conditions. For these reasons, PE is frequently missed or misdiagnosed, and is the subject of a great deal of research to help doctors understand how best to diagnose it.^[1]

Causes

Below are several conditions that promote blood clots in deep veins. These three factors are known as Virchow's triad, after Rudolf Virchow, a physician who studied DVTs.

• Damage to the inner lining of a vein. This damage may result from injuries caused by physical, chemical, and biological factors. Such factors include surgery, serious injury, inflammation, or an immune response.
• Sluggish or slow blood flow. This may occur after surgery, traveling for long periods of time, or an illness that requires lying in bed for a long time.
• Blood is thicker or more likely to clot than usual. Certain inherited conditions (such as protein C& S deficiency, factor V Leiden) increase blood's tendency to clot. This also is true of treatment with hormone replacement therapy or birth control pills.

Diagnosis

Diagnosis of DVT is based on medical history, physical exam, and the results from tests. A doctor can identify risk factors and rule out any other possible causes.

Medical history

Medical histories take note of the following:

• Overall health
• Any prescription medicines
• Any recent surgeries or injuries
• Any diagnosis of cancer

Physical exam

During the physical exam, doctors check the legs for signs of DVT, although sometimes DVTs are present without being detectable on exam. Blood pressure, heart and lungs are also examined.

Diagnostic tests

One or more tests may be needed to find out whether a DVT is present. The most common tests used to diagnose DVT are the following:

• Ultrasound. This is the most common test for diagnosing deep vein blood clots. It uses sound waves to create pictures of blood flowing through the arteries and veins in the affected leg.
• A D-dimer test. This test measures a substance in the blood that's released when a blood clot dissolves. If the test shows high levels of the substance, there may be a deep vein blood clot. If the test is normal and there are few risk factors to begin with, a DVT is unlikely. Unfortunately, the d-dimer test is not always reliable.
• Venography. This test is used if ultrasound doesn't provide a clear diagnosis. Dye is injected into a vein, and then an x-ray is taken of the leg. The dye makes the vein visible on the x-ray. The x-ray will show whether blood flow is slow in the vein. This may indicate a blood clot.

Other less common tests used to diagnose DVT include magnetic resonance imaging (MRI) and computed tomography (CT) scanning. These tests provide pictures of the inside of the body.

Blood tests may be needed to check for an inherited blood clotting disorder that can cause DVT. Inherited disorders are likely if there have been repeated blood clots that can't be linked to another cause, or if a blood clot develops in an unusual location, such as a vein in the liver, kidney, or brain.

If a PE is suspected, extra tests such as a CT scan or a ventilation-perfusion scan (V/Q scan) are performed. In a CT scan for PE, dye is injected into a vein, then a series of X-rays are taken. The V/Q scan uses a radioactive material to show how well oxygen and blood are flowing to all areas of the lungs.

Treatment

Treatment of DVT has several goals:

• Stop the blood clot from getting bigger
• Prevent the blood clot from breaking off and moving to the lungs
• Reduce the chance of having another blood clot

Medicines

Medicines are used to prevent and treat DVT.

Anticoagulants

Anticoagulants are the most common medicines for treating DVT. They're also known as blood thinners. These medicines decrease the blood's ability to clot. They also stop existing blood clots from getting bigger. However, blood thinners cannot break up blood clots that have already formed. (The body dissolves most blood clots with time.)

Blood thinners can be taken as either a pill, an injection under the skin, or through a needle or tube inserted into a vein (called intravenous, or IV, injection).

Warfarin and heparin are two blood thinners used to treat DVT. Warfarin is given in pill form. Heparin is given as an injection or through an IV tube. Warfarin and heparin are often used in combination. Heparin acts quickly. Warfarin takes two or three days before it starts to work. Once the warfarin starts to work, the heparin is stopped. Pregnant women usually are treated with heparin only, because warfarin is dangerous during pregnancy.

Treatment for DVT with blood thinners usually lasts from three to six months. The following situations may change the length of treatment:

• If the blood clot occurred after a short-term risk (for example, surgery), treatment time may be shorter.
• If there have been blood clots before, treatment time may last longer.
• If there are certain other illnesses, such as cancer, it may be necessary to take blood thinners for as long as the illness is present.

The most common side effect of blood thinners is bleeding. This happens if the medicine thins the blood too much. This side effect can be life-threatening.

Sometimes, the bleeding is internal (inside the body). People treated with blood thinners usually receive regular blood tests to measure the ability of the blood to clot. These blood tests are called PT and PTT tests, and the number measured is sometimes expressed as the INR. These tests also help a doctor make sure a patient is taking the right amount of medicine.

Thrombin inhibitors

Thrombin inhibitors are medications that interfere with the blood clotting process. They are used to treat blood clots in patients who cannot take heparin.

Thrombolytics

Thrombolytics are medications that are given to quickly dissolve a blood clot. They are used to treat large blood clots that cause severe symptoms. Because thrombolytics can cause sudden bleeding, they are used only in life-threatening situations.

Other types of treatment

Other approaches to DVT treatment are available in addition to, or instead of, medications.

Vena cava filter

A vena cava filter is used if blood thinners cannot be taken, or if a clot develops while being on blood thinners. The filter is inserted inside a large vein called the vena cava. The filter catches blood clots that break off in a vein before they move to the lungs. This prevents PE. However, it doesn't stop new blood clots from forming.

Graduated compression stockings

These stockings can reduce the swelling that may occur after a blood clot has developed in the leg. Graduated compression stockings are worn on the legs from the arch of the foot to just above or below the knee. These stockings are tight at the ankle and become looser as they go up the leg. This creates gentle pressure up the leg. The pressure keeps blood from pooling and clotting. These stockings are typically worn for at least a year after DVT is diagnosed.

Prevention

The following steps can be taken in order to prevent DVT:

• Regular checkups
• Taking all medicines that the doctor prescribes
• Get out of bed and moving around as soon as possible after surgery or illness
• Exercising the lower leg muscles during long trips

The following help prevent future blood clots from forming after a DVT:

• Taking all medicines for prevention of blood clots
• Following up with a doctor for tests and treatment
• Using compression stockings as directed to prevent swelling in the legs from DVT

Travel tips

The risk of developing DVT while traveling is small. The risk increases if the travel time is longer than four hours, or if there are other risk factors for DVT.

The precautions taken below may help reduce the risk of blood clots when traveling:

• Walking up and down the aisles of the bus, train, or airplane. If traveling by car, stopping about every hour to walk may help.
• Moving the legs and flexing and stretching the feet to encourage blood flow in the calves
• Wearing loose and comfortable clothing
• Drinking plenty of fluids and avoiding alcohol

If a person is at an increased risk for developing a DVT, the doctor may recommend wearing compression stockings during travel or taking a blood-thinning medicine before traveling.

Living With Deep Vein Thrombosis

Anyone who has had a deep vein blood clot is at greater risk for developing another one. During treatment and after, careful monitoring can improve outcome:

• Initiate procedures that prevent DVT
• Checking the legs for signs and symptoms of DVT. These include swollen areas, pain or tenderness, increased warmth in swollen or painful areas, or red or discolored skin on the legs.
• Contacting a doctor right away if signs of DVT appear

The risk of developing another blood clot is highest in the first three years following a DVT.^[2] In addition, people with a PE have a greater risk of premature death.^[2]

Ongoing health care needs

Medicines that thin the blood and prevent blood clots are used to treat DVT. These medicines can thin the blood too much and cause bleeding (sometimes inside the body). This side effect can be life-threatening.

Bleeding may occur in the digestive system or the brain. Signs and symptoms of bleeding in the digestive system include the following:

• Bright red vomit or vomit that looks like coffee grounds
• Bright red blood in the stools or black, tarry stools
• Abdominal pain

Signs and symptoms of bleeding in the brain include the following:

• Severe pain in the head
• Sudden changes in vision
• Sudden loss of movement in the arms or legs
• Memory loss or confusion

Profuse bleeding after a fall or injury may be a sign that the DVT medicines have thinned the blood too much. Taking two medicines that thin the blood may increase the risk for bleeding.

Foods that contain vitamin K can change how warfarin (a blood-thinning medicine used to treat DVT) works. Vitamin K is found in green, leafy vegetables and some oils, like canola and soybean oil. A doctor can help plan a balanced and healthy diet.

Chances of Developing a DVT

About 100 to 117 people per 100,000 develop DVT each year in the United States.^[3][4]

Many factors increase the risk for DVT. They include the following:

• History of DVT, in oneself or a family member
• Disorders or factors that make the blood thicker or more likely to clot than normal
• Injury to a deep vein from surgery, a broken bone, or other trauma
• Slow blood flow in a deep vein from lack of movement
• Pregnancy and the first six weeks after giving birth
• Recent or ongoing treatment for cancer
• A central venous catheter, or a tube placed in a vein to allow easy access to the bloodstream for medical treatment
• Older than 60 (although DVT can occur in any age group)
• Overweight or obesity

Clinical Trials

Visit here for current clinical trials on DVT.

Research

Risk factors for DVT continue to be identified. For example, particulate matter in air pollution has been shown to increase the risk of DVT.^[5] Particulate matter is very small particles of solid or liquids. An Italian study found that DVT was more likely in people exposed to a high amount of particulate air pollution.^[5]. In addition, the risk of DVT increased as the amount of air pollution increased.

Acetylsalicylic acid, or aspirin, is used at low doses to reduce the risk of cardiovascular disease and cardiovascular events, such as a heart attack. This prophylactic effect is due to the ability of the drug to thin the blood. Analysis of the Women’s Health Study showed that long-term, low-dose aspirin use did not reduce the risk of developing DVT or PE in women when compared to use of a placebo.^[6]

References

1. ↑ Segal JB, Eng J, Tamariz LJ, Bass EB. Review of the evidence on diagnosis of deep venous thrombosis and pulmonary embolism. Ann Fam Med. 2007 Jan-Feb;5(1):63-73. Abstract | Full Text | PDF
2. ↑ ^{2.0 2.1} EurekAlert. Study examines long-term outcomes following blood clots.
3. ↑ White RH. The epidemiology of venous thromboembolism. Circulation. 2003 Jun 17;107(23 Suppl 1):I4-8.Abstract | Full Text | PDF
4. ↑ Silverstein MD, Heit JA, Mohr DN, Petterson TM, O'Fallon WM, Melton LJ 3rd. Trends in the incidence of deep vein thrombosis and pulmonary embolism: a 25-year population-based study. Arch Intern Med. 1998 Mar 23;158(6):585-93. Abstract | Full Text | PDF
5. ↑ ^{5.0 5.1} EurekAlert. Air pollution may be associated with blood clots in deep leg veins.
6. ↑ Glynn RJ, Ridker PM, Goldhaber SZ, Buring JE. Effect of low-dose aspirin on the occurrence of venous thromboembolism: a randomized trial. Ann Intern Med. 2007 Oct 16;147(8):525-33. Abstract | PDF | Summary for Patients

External Links

Resources from the National Heart, Lung, and Blood Institute:

• Pulmonary Embolism (Diseases and Conditions Index)
• Study Finds Ways to Improve Detection of Blood Clots in the Lung (NIH press release, May 31, 2006)
• Low Dose Warfarin Prevents Recurrence of Blood Clots—NHLBI Stops Study (NIH press release, February 24, 2003)