← All guides · Heart, lungs and nerves tests
Exhaled nitric oxide test (FeNO)
FeNO test · exhaled nitric oxide · airway inflammation test · nitric oxide breath test
You breathe out slowly into a small device. It shows whether there is a certain type of inflammation in your airways.
When asthma is suspected, and to check how well inhaler treatment is working.
⏱ Duration: usually 5 to 10 minutes; the result is given right away
Be sure to tell your doctor
How to prepare
- Food. Usually do not eat or drink anything except water for 1 hour before. You are often asked to avoid nitrate-rich foods before the test, like beets and leafy salad. Check with the clinic.
- Smoking. Do not smoke on the day of the test.
- Exercise. No exercise for an hour before the test.
- Medicines. Do not stop your inhalers on your own. Tell your doctor when you last used them.
What to bring
- Your referral
- A list of your medicines and inhalers
How it goes
- You sit by the device
- You take a deep breath in through the mouthpiece
- You breathe out slowly and evenly for about 10 seconds
- A guide on the screen helps you keep the right force
- It is usually repeated 2 to 3 times
What you'll feel
- It does not hurt
- Sometimes it is hard to breathe out evenly. The screen guide helps
Afterwards
- The result is usually shown right away
- Your doctor will explain it along with other tests
- You can go back to your usual day right away
Common questions
Will the test show asthma?
It shows inflammation in the airways. Your doctor makes the diagnosis together with other tests.
Can children do it?
Yes, usually from age 5 or 6, if the child can breathe out evenly.