Longitudinal measurements of exhaled nitric oxide in children-what is a significant change in FE(NO) ?

The principle aim of this study was to describe the variability of exhaled nitric oxide (FE(NO)) concentrations over 10 months in children with and without asthma. FE(NO) was measured on six occasions at 2-month intervals in a community-based cohort of children with and without asthma. There were 178 children recruited, 47 had asthma, mean age 9.6 yr. A total of 851 FE(NO) measurements were made. The change in FE(NO) values was positively associated with the initial FE(NO) concentration (p < 0.001) and duration between paired measurements (p = 0.016) but not asthma diagnosis; there was an interaction between initial FE(NO) and duration between measurements. As an approximate rule-of-thumb, a child's FE(NO) may rise by up to 100% of their current FE(NO) over 2 and 4 months, independent of asthma. Both the baseline FE(NO) and interval between repeated FE(NO) measurements are relevant to FE(NO) values, independent of asthma. These findings may be useful to clinical interpretation of FE(NO) results in children.