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[Agreement between two devices for measuring exhaled nitric oxide].

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.