Measurement of FeNO is non-invasive and standardised, with results available at the point of testing. Because of the small sample size and short duration of studies, exacerbation frequencies were not measured. Despite this, the review suggests that FeNO may be a potential biomarker for assessing ICS response in COPD. Further research that stratifies patients by FeNO levels and assesses the impact on acute exacerbations is needed to understand its potential value in routine clinical practice.