Determinants of, and reference equation for, exhaled nitric oxide in the Chinese population

Measurement of fractional exhaled nitric oxide concentration (FeNO) has been proposed as a useful biomarker for monitoring and management of airway diseases. Limited information is available regarding reference levels of FeNO levels in Chinese adults. This study aimed to investigate the reference equation and determinants of FeNO in Chinese adults. 1093 (577 males) healthy nonsmoking subjects aged 18-90 years were recruited. FeNO was measured online using a chemiluminescence analyser. Other assessments included spirometry, skin prick tests, total serum IgE levels and eosinophil count in peripheral blood. The geometric mean FeNO was 32.6 (95% reference interval (RI) 31.4-33.7) ppb for all subjects. FeNO values were higher in males than females (geometric mean (95% RI) 38.3 (36.5-40.2) ppb versus 27.1 (25.8-28.5) ppb, p<0.0001), and in atopic than nonatopic subjects (34.6 (33.0-36.3) ppb versus 29.8 (28.3-31.4) ppb, p<0.0001). FeNO correlated with age (r(2) = 0.23), height (r(2) = 0.20), IgE level (r(2) = 0.18) and percentage eosinophil count (r(2) = 0.18) (all p<0.0001), but not with spirometric parameters. Based on multiple regression modelling, the reference equation of FeNO value was: log(FeNO) = 0.781 + 0.104(sex) + 0.004(age) + 0.084(atopy) + 0.003(height in cm), where for sex 1 = male and 0 = female, age is measured in years, for atopy 1 = atopic and 0 = nonatopic, and height is measured in cm. The FeNO of Chinese adults is higher than that of the Caucasian population, and is affected by age, sex, height and atopic status. This study provides useful references for the interpretation of FeNO.