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Respiratory societies recommend use of standardized methodologies for FeNO measurements in adults and children, but in pre-schoolers, feasibility remains a problem. The exhalation time needed to obtain steady-state FeNO is unclear. Our primary aim was to study the feasibility of an adapted single-breath FeNO method with age-adjusted exhalation times. We also studied the association between time to steady-state NO level and height, as well as FeNO in relation to asthma and current treatment with inhaled corticosteroids (ICS).

METHODS: Sixty-three children aged 3-10 years performed FeNO measurements with a hand-held electrochemical device with a newly developed flow-control unit. Exhalation times were pre-adapted to age. Exhaled air was simultaneously sampled to a chemiluminescence analyser to measure time to steady-state NO level.

RESULTS: Eighty-one percent of the children achieved at least one approved measurement. From 4 years upwards, success rate was high (96%). Time to steady-state [NO] (median and interquartile range) was 2.5 s (2.4-3.5) at age 3-4 years and 3.5 s (2.7-3.8) at 5-6 years. Height was associated with time to steady-state (r(2) =0.13, p=0.02). FeNO (geometric mean (95% CI)) was higher in ICS-naïve asthmatic children (n=19): 15.9 ppb (12.2-20.9), than in both healthy controls (n=8) 9.1 ppb (6.6-12.4) and asthmatic subjects on treatment (n=24) 11.5 ppb (9.7-13.6)

CONCLUSION: We found this adapted single-breath method with age-adjusted exhalation times highly feasible for children aged 4-10 years. ICS-naïve asthmatic children had FeNO levels under the current guideline cut-off level (20 ppb), highlighting the importance of taking age into account when setting reference values. This article is protected by copyright. All rights reserved.