Deep Vein Thrombosis

What Is Deep Vein Thrombosis?

Deep vein thrombosis (throm-BO-sis), or DVT, is a blood clot that forms in a vein deep in the body. Blood clots occur when blood thickens and clumps together.

Most deep vein blood clots occur in the lower leg or thigh. They also can occur in other parts of the body.

A blood clot in a deep vein can break off and travel through the bloodstream. The loose clot is called an embolus (EM-bo-lus). When the clot travels to the lungs and blocks blood flow, the condition is called pulmonary embolism (PULL-mun-ary EM-bo-lizm), or PE.

PE is a very serious condition. It can damage the lungs and other organs in the body and cause death.

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

Blood clots also can form in the veins closer to the skin's surface. However, these clots won't break off and cause PE.

What Causes Deep Vein Thrombosis?

Blood clots can form in your body's deep veins when:

  • A vein's inner lining is damaged. Injuries caused by physical, chemical, or biological factors can damage the veins. Such factors include surgery, serious injuries, inflammation, and immune responses.
  • Blood flow is sluggish or slow. Lack of motion can cause sluggish or slow blood flow. This may occur after surgery, if you're ill and in bed for a long time, or if you're traveling for a long time.
  • Your blood is thicker or more likely to clot than normal. Some inherited conditions (such as factor V Leiden) increase the risk of blood clotting. Hormone therapy or birth control pills also can increase the risk of clotting.

Who Is At Risk for Deep Vein Thrombosis?

The risk factors for deep vein thrombosis (DVT) include:

  • A history of DVT.
  • Conditions or factors that make your blood thicker or more likely to clot than normal. Some inherited blood disorders (such as factor V Leiden) will do this. Hormone therapy or birth control pills also increase the risk of clotting.
  • Injury to a deep vein from surgery, a broken bone, or other trauma.
  • Slow blood flow in a deep vein due to lack of movement. This may occur after surgery, if you're ill and in bed for a long time, or if you're traveling for a long time.
  • Pregnancy and the first 6 weeks after giving birth.
  • Recent or ongoing treatment for cancer.
  • A central venous catheter. This is a tube placed in a vein to allow easy access to the bloodstream for medical treatment.
  • Older age. Being older than 60 is a risk factor for DVT, although DVT can occur at any age.
  • Being overweight or obesity.
  • Smoking.

Your risk for DVT increases if you have more than one of the risk factors listed above.

What Are the Signs and Symptoms of Deep Vein Thrombosis?

The signs and symptoms of deep vein thrombosis (DVT) may be related to DVT itself or to pulmonary embolism (PE). See your doctor right away if you have symptoms of either. Both DVT and PE can cause serious, possibly life-threatening complications if not treated.

Deep Vein Thrombosis

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

  • Swelling of the leg or along a vein in the leg
  • Pain or tenderness in the leg, which you may feel only when standing or walking
  • Increased warmth in the area of the leg that's swollen or in pain
  • Red or discolored skin on the leg

Pulmonary Embolism

Some people don't know they have DVT until they have signs or symptoms of PE. Symptoms of PE include:

  • Unexplained shortness of breath
  • Pain with deep breathing
  • Coughing up blood

Rapid breathing and a fast heart rate also may be signs of PE.

How Is Deep Vein Thrombosis Diagnosed?

Your doctor will diagnose deep vein thrombosis (DVT) based on your medical history, a physical exam, and the results from tests. He or she will identify your risk factors and rule out other causes for your symptoms. For some people, DVT might not be diagnosed until after they receive emergency treatment for pulmonary embolism (PE).

Medical History

To learn about your medical history, your doctor may ask about:

  • Your overall health
  • Any prescription medicines you're taking
  • Any recent surgeries or injuries you've had
  • Whether you've been treated for cancer

Physical Exam

Your doctor will check your legs for signs of DVT, such as swelling or redness. He or she also will check your blood pressure and your heart and lungs.

Diagnostic Tests

Your doctor may recommend tests to find out whether you have DVT.

Common Tests

The most common test for diagnosing deep vein blood clots is ultrasound. This test uses sound waves to create pictures of blood flowing through the arteries and veins in the affected leg.

Your doctor also may recommend a D-dimer test or venography (ve-NOG-rah-fee).

A D-dimer test measures a substance in the blood that's released when a blood clot dissolves. If the test shows high levels of the substance, you may have a deep vein blood clot. If your test results are normal and you have few risk factors, DVT isn't likely.

Your doctor may suggest venography if an ultrasound doesn't provide a clear diagnosis. For venography, dye is injected into a vein in the affected leg. The dye makes the vein visible on an x-ray image. The x ray will show whether blood flow is slow in the vein, which may suggest a blood clot.

Other Tests

Other tests used to diagnose DVT include magnetic resonance imaging (MRI) and computed tomography (to-MOG-rah-fee), or CT, scanning. These tests create pictures of your organs and tissues.

You may need blood tests to check whether you have an inherited blood clotting disorder that can cause DVT. This may be the case if you have repeated blood clots that are not related to another cause. Blood clots in an unusual location (such as the liver, kidney, or brain) also may suggest an inherited clotting disorder.

If your doctor thinks that you have PE, he or she may recommend more tests, such as a lung ventilation perfusion scan (VQ scan). A lung VQ scan shows how well oxygen and blood are flowing to all areas of the lungs.

Read the rest of this article, including current treatments for DVT, as well as related materials at the National Heart, Lung and Blood Institute. You may also wish to see the HealthyNJ page on Blood Clots & Blood Thinners.

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