Testing your lungs: the gas transfer test

The main job of the lungs is to bring oxygen into your bloodstream and to remove carbon dioxide. This is called gas transfer. Certain conditions, such as chronic obstructive pulmonary disease (COPD) or idiopathic pulmonary fibrosis (IPF), can make gas transfer more difficult.

The gas transfer test estimates how well your lungs work to take oxygen from the air you breathe and put it into your bloodstream. It can be used to help diagnose and monitor a range of different lung conditions.

Last Update 16/04/2024
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When will I be tested?

Your healthcare professional will refer you for the test if they need to learn more about how well your lungs are working. If you have questions about your lung health or the gas transfer test, you will need to speak to your healthcare provider.


What happens during the test?

The test involves breathing in a small but safe amount of a gas called carbon monoxide through a mouthpiece and holding your breath for 10 seconds to see how much of it is taken up by your lungs.


What do the results mean?

A sample of the gas you breathed out in your test will be analysed by the machine. The results will tell your healthcare professional how well your lungs transfer oxygen into the bloodstream.

Your healthcare professional will compare your results to what is considered normal for a person of your age, height, sex and ethnicity.

What happens if the test results look abnormal?

Abnormal results suggest that oxygen is not moving easily from your lungs into your bloodstream. This could be due to a number of different health conditions, including idiopathic pulmonary fibrosis and COPD. Your healthcare professional will look at the results with you to understand the cause.

Many conditions that affect our lungs are caused by smoking. It is never too late to give up smoking, and there is support available – ask your healthcare professional how they can help you to quit. The European Lung Foundation website (www.europeanlung.org) has lots of information about the benefits of quitting smoking which you can download in a range of languages, so this could be a good place to start.

If you have already been diagnosed with a lung condition, your results will help you understand how best to manage it, and whether further treatments are needed. Your healthcare professional will discuss this with you.

What problems might occur during the test?

There are no known risks of doing the gas transfer test, but you may find it makes you feel tired – especially if you have a lung condition. Make sure you know what to expect before you go. You can do this by watching our video demonstration of the gas transfer test below or at www.youtube.com/watch?v=5eET_dRV284&t=4s. Knowing what to expect can save you time and energy.

You will be given time to recover between tests to make sure you do not get too tired.  If you feel tired or lightheaded, ask your healthcare professional for a few minutes to recover before trying the test again.

Some people may find that the test makes them want to cough. If this happens, try to clear your chest before you try again.

Will I need any more tests?

You may be asked to repeat the gas transfer test at different times to understand what a normal result looks like for you and to monitor your condition.

If your results suggest that you might have a lung condition, your healthcare professional may refer you for some more tests so that they can make a diagnosis.

Taking the gas transfer test video

Taking the gas transfer test