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

INTRODUCTION:Fractional exhaled nitric oxide (FE NO) may be a useful objective measurement to guide asthma treatment. What remains uncertain is what change in FE NO is clinically significant. METHODS:An individual patient data analysis was performed using data from seven randomized clinical trials which used FE NO to guide asthma treatment. The absolute and percentage intra-subject change in FE NO measurements over "stable" and also "unstable" 3-month periods were described. RESULTS: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 FE NO among individuals whose initial FE NO was <50 parts per billion (ppb) were -7 to +9 ppb and -43 to +50 ppb, and for those with initial FE NO ≥50 ppb IQR was -29 to +17 ppb and LoA was -80 to +76 ppb. For percentage change in FE NO, the IQR and LoA for individuals whose initial FE NO was <50 ppb were -33% to +51% and -157% to +215%, and for those with initial FE NO ≥50 ppb were -33% to +35% and -159% to +192%. The variation in FE NO values for a stable period was similar irrespective of whether it was followed by a stable or unstable period. CONCLUSIONS:Over a 3-month period where FE NO is initially <50 ppb, a rise of <10 ppb or of <50% (based on IQR) is unlikely to be related to asthma. When FE NO is initially ≥50 ppb an percentage change of <50% (based on IQR) is unlikely to be asthma-related.