Reproducibility of exhaled nitric oxide measurements in healthy and asthmatic adults and children

Airway inflammation in asthma is not measured routinely in clinical practice. Fractional exhaled nitric oxide (FE(NO)), a marker of airway inflammation, is increasingly used as an outcome measure in asthma intervention studies and yet the reproducibility of FE(NO) measurements is unknown. The reproducibility, day-to-day, diurnal variation and perception of standardised FE(NO) measurements were examined in 59 subjects (40 children aged 7-13 yrs and 19 adults aged 18-60 yrs), both healthy (n=30) and with mild (n = 29) asthma. FE(NO) was measured on five consecutive days (four measurements on the same day) for adults and twice on the same day for children. The coefficient of reproducibility expressed as the mean pooled standard deviation (n = 59, 675 estimations) was 2.11 parts per billion (ppb) and intraclass correlation coefficient was 0.99 in both children and adults. FE(NO) was significantly higher in asthma subjects (32.3 ppb) than in healthy subjects (16.3 ppb). There was no diurnal or day-to-day variation, or a learning effect, as the result of FE(NO) measurements were identical at results of the beginning and at the end of the study. It was concluded that fractional exhaled nitric oxide measurements are simple, reproducible, free from diurnal and day-to-day variation, and acceptable by both healthy and asthmatic adults and children, as a part of their routine visit to a physician.