Recent guidelines for the diagnosis of asthma in school children recommend the measurement of exhaled nitric oxide (FeNO) as part of the diagnostic algorithm. However, implementation may be hampered by the lack of FeNO devices that are affordable and usable in all health care settings. We aimed to compare the performance of two portable FeNO devices (Evernoa (EVE) and NObreath® (NOB)) to a stationary gold standard device (CLD 88 sp) in children.One hundred and six (106) children aged 6–17 years under investigation or monitoring for asthma underwent FeNO measurements using the three devices in randomised order. All devices showed high repeatability across a wide FeNO range (2.5–191.9 ppb). Median FeNO levels were significantly lower with the portable devices (20.8 ppb [interquartile range: 9.5–43.5], 16 ppb [9–36], 22.8 ppb [13.2–55.2] for NOB, EVE and CLD, respectively (p<0.0001). Despite the proportional bias (−20% (NOB) and −40% (EVE), both devices demonstrated good overall agreement with CLD (>94%) at a cut-off level 25 ppb but lower agreement for the cut-off 35ppb. EVE required a greater number of attempts compared to NOB and CLD to achieve 2 valid measurements.Both portable devices showed limited interchangeability with the gold standard, making them less applicable for research and disease monitoring purposes. However, good overall agreement at the ERS cut-off level suggests potential as a simple and convenient screening tool in clinical settings for initial asthma diagnosis.
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