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.

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

During the physical exam, your doctor will check your legs for signs of DVT. He or she also will check your blood pressure and your heart and lungs.

Diagnostic Tests

You may need one or more tests to find out whether you have DVT. The most common tests used to diagnose DVT are:

• 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, you may have a deep vein blood clot. If your test is normal and you have few risk factors, DVT isn't likely.
• Venography (ve-NOG-ra-fee). 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.

You may need blood tests to check whether you have an inherited blood clotting disorder that can cause DVT. You may have this type of disorder if you have repeated blood clots that can't be linked to another cause, or if you develop a blood clot in an unusual location, such as a vein in the liver, kidney, or brain.

If your doctor thinks that you have pulmonary embolism (PE), he or she may order extra tests, such as a ventilation perfusion scan (V/Q scan). The V/Q scan uses a radioactive material to show how well oxygen and blood are flowing to all areas of the lungs.

For more about tests used to diagnose PE, see the Diseases and Conditions Index Pulmonary Embolism article.