FeNO stands for Fractional Exhaled Nitric Oxide and is measured using a simple breath test.

Nitric oxide is a gas which everyone breathes out. People with inflamed airways breathe out more nitric oxide than people whose airways are not inflamed. These patients are more likely to have an asthma attack if their inflammation remains untreated.

FeNO is already measured in patients with severe asthma who are seen in hospital clinics. However, very few GP surgeries routinely use FeNO to help them monitor treatment.


A copy of the FeNO Patient Booklet can be found below:



This page was last updated: April 2023