Measurement of exhaled nitric oxide: comparison of different analysers.

Background And Objective: Exhaled nitric oxide (NO) is used as a surrogate marker to monitor eosinophilic airway inflammation, assist in diagnosis, and support treatment decisions for asthma patients. The aim of this study was to compare five NO analysers: Medisoft (M), Aerocrine Niox (N), Aerocrine Niox flex (NF), Aerocrino Niox mino (NM) and EcoMedics (E).

Methods: In 85 subjects (25 asthma patients, 25 COPD patients, 35 healthy volunteers; median age 36.5 years, range 23-79, 47% female), three NO measurements per individual were performed, using each analyser according to the American Thoracic Society/European Respiratory Society guidelines. Subjects evaluated the devices on the basis of comfort and ease of performing the measurement.

Results: Median NO concentrations were 24.8 parts per billion (ppb) (range 6.3-262.7) for M, 14.5 ppb (0.0-196.6) for N, 15.2 ppb (5.6-67.7) for NF, 16.3 ppb (5.0-208.3) for NM, and 13.1 ppb (4.0-103.0) for E. There was significant correlation among the absolute NO values measured with all the devices (0.743 for M vs NF < r < 0.979 for N vs NF). Bland-Altman plots suggested an acceptable degree of agreement among the results obtained with the three Niox analysers. Measurements obtained with the Medisoft and Ecomedics analysers were not directly comparable with those obtained with the other devices. The greatest differences in absolute NO levels for individual patients were between measurements with the M and E analysers (8.3 ppb, range 27.4-159.7, P < 0.001). Acceptance of the measurements by patients was high, independent of the device used.

Conclusions: Exhaled NO values obtained with different devices were not directly comparable and may differ to a clinically relevant extent, depending on which device is used.