Pulmonary Embolism: Diagnosis

Reviewed by the National Heart Lung and Blood Institute

To diagnose pulmonary embolism (PE), the doctor will ask about your medical history and perform a physical examination. During the physical exam, the doctor will check your legs for signs of deep vein thrombosis (DVT). He or she also will check your blood pressure and your heart and lungs.

Following these procedures, a series of diagnostic tests may be performed. A patient may have one of the following imaging tests:

  • Ultrasound. Doctors use this test to look for blood clots in your legs. Ultrasound uses high-frequency sound waves to check the flow of blood in your veins. A gel is put on the skin of your leg. Then a hand-held device called a transducer is placed on the leg and moved back and forth over the affected area. The transducer gives off ultrasound waves and detects their echoes after they bounce off the vein walls and blood cells. Following this, a computer turns the echoes of the ultrasound waves into a picture on a computer screen, where your doctor can see the blood flow in your leg. If blood clots are found in the deep veins of your legs, you will begin treatment. DVT and PE are both treated with the same medicines.

  • Spiral CT scan or CT angiogram. Doctors use this test to look for blood clots in your lungs and in your legs. Dye is injected into a vein in your arm to make the blood vessels in your lungs and legs more visible on the x-ray image. While you lie on a table, an x-ray tube rotates around you, taking pictures from different angles. This test allows doctors to detect PE in most patients. The test only takes a few minutes and results are available shortly after the scan is completed.

  • Ventilation-perfusion lung scan (VQ scan). Doctors use this test to detect PE. The VQ scan uses a radioactive material to show how well oxygen and blood are flowing to all areas of the lungs.

  • Pulmonary angiography is another test used to diagnose PE and a trained specialist must perform the test. A flexible tube called a catheter is threaded through the groin (upper thigh) or arm to the blood vessels in the lungs. Dye is injected into the blood vessels through the catheter. X-ray pictures are taken to show the blood flow through the blood vessels in the lungs. If a clot is discovered, the doctor may use the catheter to extract it or deliver medicine to dissolve it.

Other specific blood tests may help the doctor find out whether you're likely to have PE:

  • A D-dimer test measures a substance in the blood that's released when a clot breaks up. High levels of the substance mean there may be a clot. If your test is normal and you have few risk factors, PE isn't likely.

  • Other blood tests check for inherited disorders that cause clots and measure the amount of oxygen and carbon dioxide in your blood (arterial blood gas). A clot in a blood vessel in your lung may lower the level of oxygen in your blood.

To rule out other possible causes of your symptoms, the doctor may use one or more of the following tests:

  • An echocardiogram uses sound waves to check heart function and to detect blood clots inside the heart.

  • An EKG (electrocardiogram) measures the rate and regularity of your heartbeat.

  • Chest x-rays provides pictures of the lungs, heart, large arteries, ribs, and diaphragm.

  • Magnetic resonance imaging (MRI) uses radio waves and magnetic fields to make pictures of organs and structures inside the body. In many cases, an MRI can provide information that can't be seen on an x ray.

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