By how much can exhaled nitric oxide vary over three months in children with stable asthma?

Introduction: Repeated measurements of fractional exhaled nitric oxide (FeNO) may be useful objective measurements in the management of asthma. There is uncertainty in what merits a clinically-relevant change in FeNO. Methods: Individual participant data were obtained from seven randomised controlled trials where FeNO was used to guide asthma treatment. The FeNO values at the start and end of a period of stable asthma were analysed. The median absolute and percentage change in paired FeNO measurements at the start and end of a stable period were determined for individuals with a baseline FeNO of Results: Data were available in 665 children (mean age 13.1, 59%male). When the initial FeNO was Conclusions: These findings support current recommendations for interpretation of what may be a clinically relevant change in a FeNO value of ≤20ppb but for higher values, greater absolute and percentage change in FeNO values should be tolerated before any alteration in treatment is considered.