FeNO - Patient information

What is it?

Fractional exhaled nitric oxide (FeNO) is a test used to diagnose asthma by measuring your breath. The test is simple and easy to do and, alongside other diagnostic tests, can tell you and your asthma team what type of asthma you have

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.

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:

  •  Leave in plenty of time and avoid exerting yourself at least one hour before your appointment
  •  Avoid smoking at least one hour before the test
  • Hot drinks, caffeine, energy drinks and alcohol should be avoided at least one hour before the test
  • Avoid nitrate rich food such as green leafy vegetables (i.e. celery, leek, beetroot, lettuce and spinach) at least three hours before the test
You can take your regular medications as normal before the test. Ensure that the clinician is aware of any medication that has been taken before hand or if any of the activities above have taken place prior to the appointment
 

For more information, please visit: https://www.asthmaandlung.org.uk/conditions/asthma/diagnosing-asthma