What is a clinically meaningful change in exhaled nitric oxide for children with asthma?

Fractional exhaled nitric oxide (F_E NO) may be a useful objective measurement to guide asthma treatment. What remains uncertain is what change in F_E NO is clinically significant.

An individual patient data analysis was performed using data from seven randomized clinical trials which used F_E NO to guide asthma treatment. The absolute and percentage intra-subject change in F_E NO measurements over "stable" and also "unstable" 3-month periods were described.

Data were available in 1112 randomized controlled trial participants and ≥1 stable period was present for 665 individuals. The interquartile range (IQR) and limits of agreement (LoA) for change in absolute F_E NO among individuals whose initial F_E NO was <50 parts per billion (ppb) were -7 to +9 ppb and -43 to +50 ppb, and for those with initial F_E NO ≥50 ppb IQR was -29 to +17 ppb and LoA was -80 to +76 ppb. For percentage change in F_E NO, the IQR and LoA for individuals whose initial F_E NO was <50 ppb were -33% to +51% and -157% to +215%, and for those with initial F_E NO ≥50 ppb were -33% to +35% and -159% to +192%. The variation in F_E NO values for a stable period was similar irrespective of whether it was followed by a stable or unstable period.

Over a 3-month period where F_E NO is initially <50 ppb, a rise of <10 ppb or of <50% (based on IQR) is unlikely to be related to asthma. When F_E NO is initially ≥50 ppb an percentage change of <50% (based on IQR) is unlikely to be asthma-related.