Measurement of Fractional Exhaled Nitric Oxide: Comparison of Three Different Analysers

Background: Fractional exhaled nitric oxide (FeNO) is a surrogate marker for airway inflammation, supporting the diagnostic pathway and treatment decisions for asthma patients. Objectives: Aim of this study was to compare the new analyser Vivatmo pro (Bosch, BV) with NIOX VERO (Circassia, CN) and CLD (Ecomedics, EC). Methods: In 100 asthmatics (median 53 years [range 20-87], 62% female, 86% on inhaled corticosteroids [mean 1,300 mu g beclomethasone dipropionate or equivalent], 35% treated with biologics) 2 FeNO measurements per device were performed. Additionally, the success rate to achieve a valid NO value was evaluated. Results: Sixty-eight percent of the patients had FeNO values below 50 ppb. Median NO concentrations were 31 ppb (range 6-194) for BV, 33 ppb (9-164) for CN and 31ppb (7-353) for EC. Bland-Altman plots suggested an agreement within the predefined limits of +/- 5 ppb for all analysers within the therapeutically relevant range (0-70 ppb). The highest agreement in FeNO levels were between BV and EC with mean differences of -0.26 (95% CI -1.48 to 0.95) vs. 1.52 (95% CI 0.4-2.6) ppb for CN and EC. The results indicate an equivalence of the methods (two-one sided t test-equivalence test: p < 0.0001, +/- 5 ppb margins). Acceptance of the measurements was high for all devices (97%). The highest success rate to obtain 2 valid NO values without failed attempts was achieved with the BV analyser (73 vs. 62% for the CN analyser and 46% for the EC analyser). Conclusions: For the range between 0 and 70 ppb, FeNO concentrations measured with all 3 devices were statistically equivalent within predefined acceptance criteria and did not differ in a clinically relevant way.