FeNO Testing
Fractional exhaled nitric oxide (FeNO) is a test used to diagnose asthma by measuring your breath. The test is simple and easy to do.
Why is it important?
FeNO is useful to help you build a better understanding of your asthma and to manage it with the support of your asthma team. The FeNO test measures inflammation in your airways. If the inflammation is not treated it can cause life threatening asthma attacks.
By knowing what kind of asthma you have, you can:
- Understand your medication better
- Recognise when your medication is working well
- Avoid life threatening asthma attacks
How is the test done?
The FeNO test is safe and easy to do for adults and children. You will take a big breath in and then gently breath out through the filtered mouthpiece into a small portable device for approximately 10 seconds.
The test is much easier to do than other asthma tests such as spirometry or peak flow. The device shows the reading on its screen immediately.
How to prepare for the test
Ahead of the test, there are a few things that you should try to avoid to ensure that the test is effective.
Avoid exertion
Leave plenty of time and avoid exerting yourself at least one hour before your appointment
No smoking
Avoid smoking at least one hour before the test
Avoid certain drinks
Hot drinks, caffeine, energy drinks and alcohol should be avoided at least one hour before the test
Avoid nitrate-rich foods
Avoid green leafy vegetables (celery, leek, beetroot, lettuce, spinach) at least three hours before the test
Regular medication
You can take your regular medications as normal. Ensure the clinician is aware of any medication taken beforehand
Want to learn more about asthma diagnosis?
Visit Asthma + Lung UK for comprehensive information about diagnosing asthma.
Need to discuss your appointment?
If you have any questions about your FeNO test appointment, our team is here to help.