Nitric oxide is a gas produced by cells in the lungs that are involved in the inflammation associated with ‘allergic’ or ‘eosinophilic’ asthma. A FeNO test or ‘exhaled nitric oxide test‘ for someone with asthma, measures how much lung inflammation is present and how well inhaled steroid medication is suppressing this inflammation. It is a non-invasive test which does not require forced expiration.
The following demonstration shows a FeNO test being performed.