A FeNO test or exhaled nitric oxide test, in patients with allergic or eosinophilic asthma, is a way to determine how much lung inflammation is present and how well inhaled steroids are suppressing this inflammation. With allergic or eosinophilic asthma, sometimes you may feel your breathing is fine, but when you measure your exhaled nitric oxide, it may still be significantly elevated, and your physician may review your treatment to help control this inflammation.
What Is Nitric Oxide?
Nitric oxide is a gas produced by cells involved in the inflammation associated with allergic or eosinophilic asthma.
How Is Nitric Oxide Measured?
The FeNO test, which stands for the fractional concentration of exhaled nitric oxide, is performed using a portable device that measures the level of nitric oxide in parts per billion (ppb) in the air you slowly exhale out of your lungs. The exhaled nitric oxide test is different from most lung function tests in that you need to blow slowly and steadily, not hard and fast, to get an accurate measurement.
Why Is Nitric Oxide Measured?
Your respiratory physician may check your exhaled nitric oxide level to see if you have the typical inflammation associated with allergic or eosinophilic asthma during the process of establishing the diagnosis of allergic or eosinophilic asthma. Your physician may then recheck the nitric oxide level to verify the steroid inhalers you are using are suppressing the nitric oxide level.Successful control of your asthma depends upon a partnership between you and your physician. Your physician can use data from FeNO testing along with spirometry and other lung function tests to design and adjust your medication to keep your asthma under optimal control.
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Before your test
Stop reliever puffers (Ventolin, Asmol, Bricanyl) 4–6 hours before, twice-daily combination inhalers 24 hours before, and once-daily inhalers, Spiriva-type inhalers and triple-therapy inhalers (Trimbow, Breztri, Trelegy) 36–48 hours before — longer for bronchial provocation testing. No smoking or vaping for 1 hour, no alcohol for 8 hours, no vigorous exercise for 1 hour and no large meal for 2 hours before the test. Bring all your inhalers and a list of your medicines. Do not stop a medicine you need to stay safe — if in doubt, take it and tell us. Full preparation guide and printable instructions →
After your test
Your tests are performed by a respiratory scientist and reported by one of our respiratory physicians. The report is sent to your referring doctor within two weeks. If your GP referred you for the tests only, your GP goes through the results with you and can ask us for a consultation if the report recommends one; if you are already seeing one of our physicians, the results are discussed at your next appointment. If you have not heard from your doctor three weeks after the test, call (03) 9422 0077.