Exhaled nitric oxide for the diagnosis of asthma in children and adults: a systematic review

The fraction of exhaled nitric oxide (FeNO) is a marker of eosinophilic inflammation, which is associated with some forms of asthma. Asthma is currently diagnosed using a pathway of tests including spirometery, airway reversability (response to bronchodilator or course of inhaled corticosteroids (ICS)) and airway hyper-responsiveness (e.g. methocholine challenge). FeNO may be a useful diagnostic test in this pathway. This systematic review aimed to identify and synthsise evidence rating to the diagnostic accuracy of FeNO for asthma with a UK focus. We looked at the highest sum of sensitivity and specificity, as well as evidence about the potential for FeNO to be used as a rule-in test (high-specificity) or as a rule-out test (high-sensitivity).