Pulmonary embolism - Diagnosing pulmonary embolism

Diagnosing a pulmonary embolism can be difficult because the signs and symptoms vary between individuals and are common to many other conditions.

Around half of all people who develop a pulmonary embolism do so while they are in hospital. 

The condition may be suspected if:

• you have one or more associated risk factors, such as being over 60 years of age or having previously had a blood clot
• you have a blood clot in one of your legs, known as deep vein thrombosis (DVT)
• there is no other likely explanation for your symptoms

It is important that pulmonary embolisms are diagnosed correctly because treating them is not always easy and the treatments used can cause side effects.

Tests

There are a number of tests that may be carried out to help determine if you have a pulmonary embolism or rule out other causes of your symptoms.

For example, you may have a chest X-ray or tests to check how well your lungs are working. You may also have some of the more specialised tests discussed below.

Blood tests

Blood tests can be carried out to detect a number of signs of pulmonary embolism. One of the main tests looks for a substance called D-dimer.

D-dimer is a protein found in the blood after a blood clot has broken down. A D-dimer test can be used to help diagnose blood clotting abnormalities such as thrombosis (where a blood clot develops in a blood vessel).

If a blood test reveals high levels of D-dimer, it suggests that pieces of blood clot are loose in your bloodstream and may have become lodged in your pulmonary artery.

Computerised tomography pulmonary angiography

During a computerised tomography pulmonary angiography (CTPA), you are injected with a special dye before a computerised tomography (CT) scan is carried out. This dye makes it easier to see the blood vessels in your lungs during the scan.

A CT scan involves taking a series of X-rays to create a very detailed image of the inside of your body. If there is a pulmonary embolism in one of your lungs, it may show up as a gap in your blood supply during this scan.

Ventilation-perfusion scan

A ventilation and perfusion scan is used to examine the flow of air and blood in your lungs.

Before the scan, you will be asked to inhale a tasteless, odourless and slightly radioactive gas through a mouthpiece. This gas helps highlight the air flow in your lungs during the scan.

You will also be given an injection containing a small amount of radioactive material to highlight the blood vessels in your lungs during the scan.

If the scan shows parts of your lungs have air in them but no blood supply, it may be the result of a pulmonary embolism.