Performance of two portable exhaled nitric oxide fraction devices compared to a "gold standard" chemiluminescence device

Background: Recent guidelines for the diagnosis of asthma in schoolchildren recommend the measurement of exhaled nitric oxide fraction (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 healthcare 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 (CLD)) in children. Methods: 106 children aged 6-17 years under investigation or monitoring for asthma underwent FENO measurements using the three devices in randomised order. Results: All devices showed high repeatability across a wide FENO range (2.5-191.9 ppb). Median (interquartile range) F ENO levels were significantly lower with the portable devices (20.8 (9.5-43.5), 16 (9-36) and 22.8 (13.2-55.2) ppb for NOB, EVE and CLD, respectively; p<0.0001). Despite the proportional bias (-20% (NOB) and -40% (EVE)), both portable devices demonstrated good overall agreement with CLD (>94%) at a cut-off level of 25 ppb but lower agreement for a cut-off of 35 ppb. EVE required a greater number of attempts compared to NOB and CLD to achieve two valid measurements. Conclusions: 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 European Respiratory Society cut-off level (25 ppb) suggests potential as a simple and convenient screening tool in clinical settings for initial asthma diagnosis.