Reference Ranges for Exhaled Nitric Oxide Fraction in Healthy Japanese Adult Population

ABSTRACTBackgroundThe measurement of the exhaled nitric oxide fraction (FEno) is proposed as a useful marker of airway inflammation. In healthy adults, there have been a few studies of the reference ranges for FEno in Caucasians. A community study in other regions may reveal any possible ethnic differences in the FEno levels.MethodsA total of 240 healthy adults aged between 18 to 74 years were recruited from four medical centers in Japan. Current smokers and subjects having a history of atopic disease were not included. FEno was measured using an online electrochemical nitric oxide analyzer according to the current guidelines. The reference ranges for FEno were estimated using two different statistical methods recommended by International Federation of Clinical Chemistry and Laboratory Medicine.ResultsThe mean FEno was 16.9 ppb (parts per billion) with a 95% prediction interval (2.5 to 97.5 percentiles) of 6.5 to 35.0 ppb in healthy Japanese adults. Normality assumptions were met for the logarithm- transformed FEno. The geometric mean FEno was 15.4 ppb with a mean ± two standard deviations of 6.5 to 36.8 ppb. Age, gender, height, and past smoking history were not associated with the FEno levels.ConclusionsThe reference ranges for FEno in healthy Japanese adults were similar to those of Caucasians. It seems reasonable that the upper limit of FEno for healthy adults should be set at approximately 36.0 ppb irrespective of ethnic differences.