A comparison of exhaled nitric oxide measurements performed using three different analysers

Summary 

Introduction

Exhaled nitric oxide (NO) is an established technique for monitoring airway inflammation. We have compared exhaled NO measurements from 3 different analysers; Ecomedics (E), Niox (N) and Logan (L).

Methods

Thirty subjects (10 non-smoking healthy subjects, 10 non-smoking patients with asthma and 10 ex-smoking COPD patients) performed 3 repeated measurements of exhaled NO at a flow rate of 50ml/s on each of the 3 analysers. Within analyser variability was determined by calculating the repeatability coefficient for each analyser. Differences between analysers were assessed by (1) the differences between group means and (2) the Bland Altman method to estimate the variability expected for an individual using the 3 analysers.

Results

The repeatability coefficients (expressed as ratios) were 1.12, 1.19 and 1.19 for N, E and L, respectively. There were significant differences between analysers; the Logan analyser gave the highest group mean values and Ecomedics gave the lowest group mean values. Differences between analysers were observed in all subject groups (healthy, asthma, COPD). Similar results were obtained in the 3 groups when analysed separately. Bland Altman analysis gave the following ratios [data are mean ratio (95% limits of agreement)]; N:E 1.59 (1.02–2.50), L:N 1.23 (0.72–2.13), L:E 1.96 (1.09–3.57).

Conclusion

Our findings indicate that exhaled NO measurements in healthy subjects and patients with airways disease differ according to the type of analyser used.

Keywords: Exhaled nitric oxide, Chronic obstructive pulmonary disease, Asthma

Abbreviations: COPD, chronic obstructive pulmonary disease, FEV₁, forced expiratory volume in 1s, NO, nitric oxide, ppb, parts per billion, ppm, parts per million