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FeNO Test
A FeNO test measures nitric oxide in your breath, a marker of a certain type of airway inflammation, used to help diagnose and manage asthma.
Quick answer
FeNO Test: what it is and what the results mean
The FeNO (fractional exhaled nitric oxide) test measures the level of nitric oxide gas in your breath. Raised levels can indicate a type of inflammation in the airways that is often linked to asthma and responds to steroid treatment.
- Why it is done: It is used to help diagnose asthma, to identify the type of airway inflammation, and to help guide and monitor treatment, including how well inhaled steroids are working.
- Understanding results: A higher FeNO suggests the type of airway inflammation seen in asthma and supports the diagnosis or indicates a need to review treatment.
What it is
The FeNO (fractional exhaled nitric oxide) test measures the level of nitric oxide gas in your breath. Raised levels can indicate a type of inflammation in the airways that is often linked to asthma and responds to steroid treatment.
Why it is done
It is used to help diagnose asthma, to identify the type of airway inflammation, and to help guide and monitor treatment, including how well inhaled steroids are working.
What to expect
You breathe out steadily into a handheld device for around 10 seconds, following the on-screen guide. It is simple and painless; you may repeat it a couple of times for a reliable reading. It takes only a few minutes.
Understanding the results
A higher FeNO suggests the type of airway inflammation seen in asthma and supports the diagnosis or indicates a need to review treatment. A low level makes this type of inflammation less likely, though it does not exclude all asthma.
Good to know
Risks and limitations
It is completely safe and non-invasive. Results can be affected by recent food, smoking, colds and some medicines, and it reflects one type of inflammation, so it is used alongside other asthma tests.
Education and reference only. This explains the test in general terms and is not medical advice. Always follow the specific instructions from the team arranging your test, and discuss your results with your clinician.
Answers
FeNO Test: frequently asked questions
What does a high FeNO result mean?
It suggests a type of airway inflammation often seen in asthma that tends to respond to inhaled steroids. It supports the diagnosis and can guide treatment, interpreted alongside your symptoms and other tests.
Can anything affect my FeNO reading?
Yes. Recent eating, smoking, a cold, and some medicines can affect the result, so you may be given instructions beforehand, and the reading is interpreted alongside your other tests.
Related tests
Other other investigations
Sources
Where this is drawn from
- NHS — Tests and treatments
- NICE — diagnostic guidance
- Relevant royal college / professional body
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