What is a gas transfer test?
The gas transfer test is a type of breathing test to see how well oxygen passes from your lungs to your blood.
It’s used to help monitor and manage lung conditions including COPD (chronic obstructive pulmonary disease).
It may also be used to check how well your lungs are working. This could be to see if you’re well enough for surgery or how well treatments like chemotherapy are working.
How do I prepare for the gas transfer test?
You’ll get an appointment letter telling you how to prepare for your gas transfer test.
You may be asked to:
- take all your regular medicines or inhalers as normal. Sometimes you may be asked not to take them in the 24 hours before the test.
- wear loose, comfortable clothes
- avoid too much physical activity or exercise at least 30 minutes before the test
- not eat a large meal for up to two hours before the test
- not drink caffeine, like tea and coffee for up to 24 hours before the test
- not smoke or vape for up to 24 hours before the test
- not drink alcohol for up to 24 hours before the test
How does the gas transfer test work?
You’ll be given a nose clip to wear and then asked to:
- take a deep breath in through a mouthpiece
- hold your breath for up to 10 seconds
- breathe out slowly into the machine.
After resting for a few minutes, you’ll do the test again to check the results are the same. It’s normal for it to take a few attempts to get a reading.
The air you breathe in through the mouthpiece has very small amounts of carbon monoxide (CO) and helium added. This is completely safe.
The whole test takes around 10 to 30 minutes.
Are there any risks?
The test is very safe, but some people can feel tired, dizzy or cough more than usual. These feelings should pass quickly.
Tell your healthcare professional if you need more time to rest after the test.
Gas transfer test results
Your healthcare professional will compare your results to the average results for your age, height, sex, and ethnicity.
A low result may mean that oxygen is not moving easily from your lungs into your blood. This may be because of:
- thickening of air sacs in the lungs (alveoli) caused by pulmonary fibrosis
- damage to alveoli caused by emphysema
- a pulmonary embolism or pulmonary hypertension.
Understanding your results
Your healthcare professional will discuss your results with you and explain the next steps.
If your results are sent to you by letter, they may include initials.
They’re the measurements to help work out how much CO your lungs can move into your blood (TLCO), and how quickly (KCO). The results will also show how many of the tiny air sacs in your lungs are working well (VA).
Speak to your healthcare professional if you have any questions about your results.
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