Background: The fraction of exhaled nitric oxide (FeNO) is a useful marker of eosinophilic airway inflammation in asthmatics. Clinical application of FeNO measurement in Japan is expected increase because the procedure is now covered through health insurance. However, the measurement system used is known to affect FeNO results, and it remains unknown whether results from offline methods correlate with those from traditional online methods, such as NO breath®.
Methods: The study population comprised 48 patients at our hospital. FeNO levels were measured by using two offline methods (Sievers and CEIS) and a standard online method, NO breath®
Results: FeNONO breath levels were significantly correlated with FeNOSievers(r=0.875) and FeNOCEIS(r=0.888) levels. FeNONO breath levels were nearly equal to FeNOSievers results (FeNONO breath=1.05×FeNOSievers), but both of these levels were lower (p=0.02) than FeNOCEIS data (FeNONO breath=0.74×FeNOCEIS). A Bland-Altman plot of values obtained by the NO breath® and Sievers methods revealed that the NO breath® result was lower than the Sievers level when FeNO was low but was higher than the Sievers level when FeNO was high.
Conclusion: Differences exist in the levels of FeNO measurement by three methods (two offline methods and NO breath®): conversion equations are needed to compare the FeNO levels obtained by using these three methods. In addition, NO breath® may be more useful to distinguish asthmatic patients from non-asthmatics, compared with Sievers method.