Reproducibility of exhaled nitric oxide (FENO) measurements in healthy subjects

UNLABELLED: The aim of the study was to evaluate the short-term variability of FENO in healthy subjects. METHODS: 33 healthy volunteers (26 F, 7 M) aged 32.6 +/- 9.5 yrs with body mass index (BMI) of 23.3 +/- 3 kg/m2 participated in the study. Exhaled nitric oxide was analyzed on 5 consecutive days with a chemiluminescence analyzer (NIOX, Aerocrine, Sweden) according to the ATS recommendations. The exhalation flow was between 0.045 and 0.055 l/s. The measurements were performed at the same time of the day and the subjects were asked to refrain from eating and drinking for at least one hour before the analysis. RESULTS: The mean value of FENO for the whole group was 13.9 +/- 5.4 ppb, there were no correlations between FENO and age, BMI, sex or the concentration of ambient nitric oxide. Day-to-day coefficient of variation was 13.3 +/- 5.3% (range 4.6 - 23.9%), the value of pooled SD - 2.1 ppb and ICC (intraclass correlation coefficient) was 0.84. No relationship was observed between variability of FENO and intervals between measurement of exhaled nitric oxide and intake of food or beverages. CONCLUSION: Chemiluminescence analysis of FENO with NIOX is a highly reproducible method, however one has to take into account the possibility of about 13% variability of FENO within 5 days.