Background: Measurement of fractional exhaled nitric oxide (FENO) is a non-invasive marker of eosinophilic airway inflammation that can be useful in asthma diagnosis and control, as well as in treatment monitoring.
Objective: We studied the correlation between two techniques for measuring FENO: the chemiluminescence-based analyzer (NIOX, Aerocrine, Sweden) and a new portable electrochemical sensor-based analyzer (NIOX-MINO, Aerocrine).
Material and methods: FENO was measured by the single breath on-line method. In all children, three consecutives measurements were obtained with NIOX, with a maximum of six attempts, and the arithmetic mean was calculated. Next, using NIOX-MINO, a single measurement was made successively in each of the children. The variables analyzed were sex, age, height, weight, diagnosis, treatment, NIOX-MINO value, mean of three values obtained with NIOX and the NO elimination rate (nL/min). For the statistical analysis, the Bland-Altman plot was used to compare the means and the differences between measurements of FENO from NIOX and NIOX-MINO. The agreement between the two analyzers was estimated by Cohen's Kappa statistic.
Results: Thirty children were included, 14 (46.67%) boys and 16 (53.33%) girls. The mean age was 11.3+/-3.09 years. All of the children successfully performed the measurements with two analyzers. The relationship between the means and the differences in the values obtained with NIOX-MINO and NIOX were statistically significant (p<0.005). In addition, Cohen's Kappa statistic (0.78) suggested a high degree of agreement between the results obtained with the two devices.
Conclusions: The two analyzers, NIOX-MINO and NIOX, were not equivalent. There was good agreement between the FENO values measured with the two devices. Measurement of FENO with the portable electrochemical sensor-based analyzer (NIOX-MINO) is valid and feasible in children older than 5 years.