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Short-term repeatability of fractional exhaled nitric oxide (FENO) measurement in children

Introduction: F E NO measurement has a very good repeatability in clinical setting. Less is known about F E NO reproducibility in epidemiological studies. The aim of the study was to assess short-term repeatability of F E NO levels and its correlates in children aged 6-9, participants in respiratory epidemiology survey. Methods: F E NO was measured before spirometric test using portable device (NIOX MINO) on two sessions one week apart in 101 children, examined at local schools. Children9s respiratory status as assessed by ISSAC questionnaire revealed 76 children without respiratory symptoms (H), 14 with symptoms of chest wheeze or attacks of dyspnea (S), 11 with asthma diagnosed by physician (A). The relative (%) F E NO difference and concordance correlation coefficient (CCC) were used to assess F E NO repeatability. Results: Repeated F E NO levels obtained on two occasions were strongly correlated (CCC= 0.98; p E NO values were 12.6, 17.3, 29.1 ppb, (difference: p=0.08) on first occasion, 13.0, 17.7, 30.6 ppb, (difference: p=0.03) on second occasion, respectively and relative difference was 12.8%, 8.8%, 7.5%, respectively. The difference exceeding 10% was found in 36%, 5% and 2% of children, result exceeding 20% was found in 15%, 3% and 1% of children, respectively. Repeatability of F E NO levels >35 ppb was also very good (Kappa value >0.9 in all groups). Linear regression analysis did not show any effects of gender, age, height, respiratory status or lung function on F E NO relative difference. Conclusions: In population-based setting F E NO measurements are reproducible in children. The method can add to phenotyping of subjects in respiratory epidemiology studies.