Measurement of fractional exhaled nitric oxide by a new portable device: comparison with the standard technique.

Background: Fractional exhaled nitric oxide (FeNO) measurement is a reliable, noninvasive marker of airway inflammation. The use of portable FeNO analyzers may enable the assessment of airway inflammation in primary care.

Objective: The authors compared FeNO values obtained by a new portable device (NObreath, Bedfont, UK) to those of the standard stationary analyzer (NIOX, Aerocrine, Sweden) in a large cohort of asthmatic patients.

Methods: One hundred and fifty-four (age range: 14-83 years, forced expiratory volume in one second [FEV(1)] range: 48-134% predicted, asthma control test [ACT] range: 7-25) out of 168 recruited patients completed the study. Each patient performed at least two valid FeNO measurements at a constant flow rate of 50 ml/s on each of the two analyzers.

Results: A significant relationship between the FeNO values obtained by the two devices (r = .95, p < .001) was found. Altman-Bland plot confirmed this agreement. Within-patient repeatability was excellent in both devices. Intraclass correlation coefficients for NIOX and NObreath values were .925 and .967, respectively. By means of receiver operating characteristic curve analysis, the FeNO cutoff points that better identified patients with ACT ≥ 20 were 15 ppb (0.84 sensitivity and 0.42 specificity) by NIOX and 25 ppb (0.53 sensitivity and 0.69 specificity) by NObreath. Easiness to use of both devices, assessed by visual analogue scale was not different.

Conclusion: FeNO measurements obtained by the new portable FeNO analyzer are reliable because they are directly comparable with those obtained by the stationary standard device. The use of portable instruments may facilitate the FeNO measurement in primary care.