A prospective trial comparing two handheld devices to measure fractional exhaled nitric oxide to the “gold-standard-technique”.

<bold>Background & Aim:</bold> Fractional exhaled nitric oxide (FeNO) is a biomarker for asthma diagnosis. FeNO measurements were used in hospitals and for research due to expensive chemiluminescence devices. We compared Evernoa®, a new electrochemical portable handheld device, to established devices NObreath® and ECO MEDICS®. <bold>Methods:</bold> 106 children aged 6-17 years had FeNO measured using all three devices. Devices were used in randomized order and for every patient two technically acceptable measurements were performed according to the ATS/ERS guidelines. <bold>Results:</bold> All three instruments showed high repeatability (ICC > 0.98) over a wide range of FeNO values (2.5-191.9 ppb). Bland-Altman and Passing-Bablok analysis showed a proportional bias for both NObreath® and Evernoa compared to ECO MEDICS®, with 0.8 times (LoA 0.45-1.19) and 0.7 times lower (LoA 0.39-0.97) lower readings on average, respectively. When assessing agreement against the clinical cut-off level of 25 ppb (ERS guidelines) to diagnose asthma, both handheld devices demonstrated comparable and good overall agreement (>94%). However, applying the NICE cut-off (35 ppb) showed a decrease in overall agreement for the Evernoa device (86%) and a decrease in positive agreement for both devices (NObreath: 86%, Evernoa: 65%). <bold>Conclusion:</bold> In this study, the two handheld devices NObreath and Evernoa demonstrated strong correlation with the ECO MEDICS® reference at lower FeNO thresholds recommended by ERS. However, higher variability at increased FeNO levels suggests that the devices are not interchangeable with the gold standard for research and disease monitoring. It is still be relevant for clinical application.