Diagnosis

Pulmonary embolism can be difficult to diagnose, especially in people who have underlying heart or lung disease. For that reason, your doctor will likely discuss your medical history, do a physical exam, and order one or more of the following tests.

Blood tests

Your doctor may order a blood test for the clot-dissolving substance D dimer. High levels may suggest an increased likelihood of blood clots, although many other factors can also cause high D dimer levels.

Blood tests also can measure the amount of oxygen and carbon dioxide in your blood. A clot in a blood vessel in your lungs may lower the level of oxygen in your blood.

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 test known as duplex ultrasonography (sometimes called duplex scan or compression ultrasonography) uses sound waves to scan the veins in your thigh, knee and calf, and sometimes in your arms, to check for deep vein blood clots.

A wand-shaped device called a transducer is moved over the skin, directing the sound waves to the veins being tested. These waves are then reflected back to the transducer to create a moving image on a computer. The absence of clots reduces the likelihood of deep vein thrombosis. If clots are present, treatment likely will be started immediately.

CT pulmonary angiography

CT scanning generates X-rays to produce cross-sectional images of your body. CT pulmonary angiography ? also called CT pulmonary embolism study ? creates 3D images that can detect abnormalities such as pulmonary embolism within the arteries in your lungs. In some cases, contrast material is given intravenously during the CT scan to outline the pulmonary arteries.

Ventilation-perfusion scan (V/Q scan)

When there is a need to avoid radiation exposure or contrast from a CT scan due to a medical condition, a V/Q scan may be performed. In this test, a tracer is injected into a vein in your arm. The tracer maps blood flow (perfusion) and compares it with the airflow to your lungs (ventilation) and can be used to determine whether blood clots are causing symptoms of pulmonary hypertension.

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 has 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 and 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.

In some people, this procedure may cause a temporary change in heart rhythm. In addition, the dye may cause increased risk of kidney damage in people with reduced kidney function.

MRI

MRI is a medical imaging technique that uses a magnetic field and computer-generated radio waves to create detailed images of the organs and tissues in your body. MRI is usually reserved for pregnant women (to avoid radiation to the fetus) and people whose kidneys may be harmed by dyes used in other tests.