Reference values of exhaled nitric oxide in healthy Asian children aged 5 to 18 years.

This study was undertaken to establish reference values of exhaled nitric oxide fraction (F(eNO)) and its determinants in healthy Asian children. 693 healthy Asian children aged 5-18 yrs were assessed using a single-breath online F(eNO) measurement (exhaled flow 50 mL·s(-1)), questionnaires, anthropometric measurements, spirometry and total and specific immunoglobulin (Ig) E. Geometric mean F(eNO) and the upper 95% CI were 13.7 ppb and 49.7 ppb, respectively, for healthy children, and 11.2 ppb and 30.2 ppb, respectively, for those without allergic sensitisation. F(eNO) was positively associated with age, allergic sensitisation, total IgE, ambient nitric oxide, measurement in the afternoon, and drinking water within 1 h before testing, and was negatively associated with weight. In healthy children without allergic sensitisation, age was the single best explanatory variable. The F(eNO) predicted values were 1-2 ppb higher in Asian than in Caucasian children in earlier studies, while the upper 95% CI were 9-10 ppb higher. In conclusion, the upper limits of normal F(eNO) in Asian children depend on age, from 21 ppb in young children to 39 ppb in adolescents. Ethnicity, age, allergic sensitisation, total IgE, ambient nitric oxide, time of testing, drinking water and weight are important determinants.