How is a pulmonary embolism diagnosed?

It’s important doctors confirm you have a pulmonary embolism because if left untreated, a pulmonary embolism can be life threatening.

But it can be hard to confirm if you have a pulmonary embolism because the symptoms are similar to many other conditions.

If your doctor thinks you have a pulmonary embolism, they should assess you quickly to confirm the diagnosis. They'll ask you about your medical history and examine you.

If your doctor suspects you have a pulmonary embolism or a DVT, they'll calculate a Wells score. This is a score to understand your risk of pulmonary embolism. Depending on your score, your doctors will carry out tests to help confirm a diagnosis. 

This is a blood test to look for a protein called D-dimer. D-dimer helps to break down blood clots and can be found in your blood when you‘ve had a significant blood clot. If the result of your D-dimer test is negative, then it's very unlikely that you have a significant blood clot in your veins.

The results of this blood test are most useful when you’ve had other tests as well to confirm whether you have a pulmonary embolism. This is because the D-dimer test cannot show where the blood clot is in your body.

A computerised tomography pulmonary angiography (CTPA) is a test to look at the blood vessels in your lungs. You'll have a series of x-rays taken of your lungs, which can help your doctor see if you have any blockages or blood clots in your lungs.  

During the test, you'll be injected with a dye that helps to show your blood vessels. Usually, you'll be awake during the test, but you may be given medicine to help you relax.

A ventilation-perfusion scan, also called a V/Q scan or isotope lung scanning, is a test to check the flow of air and blood in your lungs. There are two parts to this test:

1. A ventilation scan - you'll be asked to breathe in air mixed with a small amount of slightly radioactive gas. The gas does not smell or taste of anything. You'll be given the gas mixed with air through a face mask and pictures will be taken of your lungs to look at the flow of air in your lungs.
2. A perfusion scan - you'll be injected with a small amount of a slightly radioactive material into a vein in your hand or arm. This injection will allow the radiographer to take a set of pictures of your lungs. The pictures will show the flow of blood in your lungs.

If these scans show parts of your lungs have air in them but no blood supply, this may mean you have a pulmonary embolism.

The radioactivity in this test is considered low risk to adults. And the benefits of confirming a pulmonary embolism outweigh the risks of the radioactivity in the test. This is because a pulmonary embolism can be life threatening if it is not treated quickly. However, people who are, or might be, pregnant should tell the radiographer. If you’re feeling worried about this test, speak to your doctor or call our helpline for advice and support. 

If your doctor thinks you have a deep vein thrombosis (DVT) which can cause a pulmonary embolism, your doctor may do a leg vein ultrasound.

During the test, your doctor will apply gel to your leg and use an ultrasound probe to press down on the veins in your leg, from your groin to your ankle. This can help work out if you have a blood clot and if you do, where it is in your leg.