Tests and diagnosis

By Mayo Clinic Staff

Pulmonary embolism can be difficult to diagnose, especially in people who have underlying heart or lung disease. For that reason, your doctor may order a series of tests to help find the cause of your symptoms. Your doctor may order one or more of the following tests.

Blood tests

Your doctor may order a blood test for the clot-dissolving substance D dimer in your blood. High levels may suggest an increased likelihood of blood clots, although D dimer levels may be elevated by other factors, including recent surgery.

In addition, blood tests may be done to determine whether you have an inherited clotting disorder.

Chest X-ray

This noninvasive test shows images of your heart and lungs on film. Although X-rays can't diagnose pulmonary embolism and may even appear normal when pulmonary embolism exists, they can rule out conditions that mimic the disease.

Ultrasound

A noninvasive "sonar" test known as duplex ultrasonography (sometimes called duplex scan or compression ultrasonography) uses high-frequency sound waves to check for blood clots in your thigh veins. In this test, your doctor uses a wand-shaped device called a transducer to direct the sound waves to the veins being tested. These waves are then reflected back to the transducer and translated into a moving image by a computer. The absence of the presence of clots reduces the likelihood of DVT. If clots are present, treatment likely will be started immediately.

CT scan

Regular CT scans take X-rays from many different angles and then combine them to form images showing 2-D "slices" of your internal structures. In a spiral (helical) CT scan, the scanner rotates around your body in a spiral — like the stripe on a candy cane — to create 3-D images. This type of CT can detect abnormalities in the arteries in your lungs with much greater precision, and it's also much faster than are conventional CT scans. In some cases, contrast material is given intravenously during the CT scan to outline the pulmonary arteries.

V/Q lung scan

This test uses small amounts of radioactive material to study airflow (ventilation) and blood flow (perfusion) in your lungs. For the first part of the test, you inhale a small amount of radioactive material while a camera that's able to detect radioactive substances takes pictures of the movement of air in your lungs. Then a small amount of radioactive material is injected into a vein in your arm, and pictures are taken as the blood flows into the blood vessels of your lungs. Comparing the results of the two studies helps provide a diagnosis.

Pulmonary angiogram

This test provides a clear picture of the blood flow in the arteries of your lungs. It's the most accurate way to diagnose pulmonary embolism, but because it requires a high degree of skill to administer and carries potentially serious risks, it's usually performed when other tests fail to provide a definitive diagnosis.

In a pulmonary angiogram, a flexible tube (catheter) is inserted into a large vein — usually in your groin — and threaded through your heart into the pulmonary arteries. A special dye is then injected into the catheter, and X-rays are taken as the dye travels along the arteries in your lungs.

A risk of this procedure is a temporary change in your heart rhythm. In addition, the dye may cause kidney damage in people with decreased kidney function.

MRI

MRI scans use radio waves and a powerful magnetic field to produce detailed images of internal structures. Because MRI is expensive, it's usually reserved for pregnant women and people whose kidneys may be harmed by dyes used in other tests.

Jan. 02, 2014

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