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GP service

NIOX FeNO asthma testing

FeNO is the testing of nitric oxide levels in breath.

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FeNO is a straightforward test to see how much nitric oxide is in your breath. Nitric oxide is often found in high quantities in the breath of people who have sensitive airways, and can therefore be useful in diagnosing asthma. The measurements from a FeNO test can also help your doctor to check that the medication you are taking is working effectively.


Using a filtered mouthpiece, you will be asked to breathe in deeply and then breathe out little by little until your lungs are empty, normally after 12 seconds. You may have to repeat this a few times.

The monitor will display the results in parts per billion (ppb) of nitric oxide in your breath.

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