Agreement and Repeatability of Three Fractional Exhaled Nitric Oxide Analyzers in Patients with Chronic Obstructive Pulmonary Disease: A Prospective Comparative Study

Background and aim: Fractional exhaled nitric oxide (FeNO) is a non-invasive biomarker of airway inflammation that may provide complementary information on inflammatory phenotypes in chronic obstructive pulmonary disease (COPD). The increasing availability of portable FeNO analyzers requires assessment of their reproducibility and agreement before measurements obtained with different devices can be considered interchangeable. In this study, we aimed to compare the performance of three FeNO analyzers in patients with COPD. Methods: In this prospective study, consecutive patients with COPD underwent FeNO assessment using three analyzers: Medisoft Hyp’Air FeNO, Sunvou CA2122, and Sunvou TM2120. Two consecutive valid measurements were obtained with each device. Both within-device repeatability and between-device agreement were evaluated, while the number of measurement attempts recorded for each analyzer was investigated as an exploratory analysis of feasibility. Results: In total, 56 participants (69.6% male), with a mean age of 70.8 ± 4.3 years and a mean FEV1 of 42.3 ± 13.1% predicted, were enrolled. All analyzers showed excellent within-device repeatability, with ICCs of 0.976 for Hyp’Air, 0.967 for CA2122, and 0.992 for TM2120. Between-device absolute agreement was highest for Hyp’Air versus TM2120 (ICC 0.989), followed by CA2122 versus TM2120 (ICC 0.943) and Hyp’Air versus CA2122 (ICC 0.931). The median number of attempts was 4.5 [3.8–5.0] with Hyp’Air, 3.0 [2.0–3.0] with CA2122, and 2.0 [2.0–3.0] with TM2120 (overall p < 0.001). Conclusions: All three FeNO analyzers demonstrated excellent within-device repeatability in patients with COPD. TM2120 showed closer agreement with Hyp’Air than CA2122, although the limited representation of elevated FeNO values prevents firm conclusions regarding inter-device agreement at higher concentrations.