OBJECTIVETo learn the normal values of exhaled nitric oxide (eNO) in children.

METHODSchool children in Beijing from 11 to 18 years of age were included in the study. All the students were assigned into two groups: normal group and abnormal group (with allergic disease) according to the International Study of Asthma and Allergy in Childhood questionnaires. eNO, peak expiratory flow rate and sensitization were measured.

RESULTTotally 395 students were screened out as normal subject (male: 177, female: 218). The eNO level was not significantly different between genders (P > 0.05), but was associated positively with age in both male and female group (P = 0.008 and P = 0.05 respectively) and associated with height in male students (P = 0.02). The geometric mean value of eNO was 11.22 ppb (parts per billion, ppb = 10(9)) in children aged from 11 to 14 years and 14.13 ppb in children aged from 14 to 18 years, with 95% confidence interval 4.17 - 30.20, 5.50 - 36.31 ppb. The eNO level was significantly increased in children who "ever had asthma or wheezing" (n = 68), and children who "ever had rhinitis" (n = 96) compared with normal subjects (P = 0.001 and P = 0.008). The geometric mean value of eNO was 16.98 ppb in children with positive skin prick test and was significantly increased as compared with children with negative skin prick test with eNO level at 11.75 ppb (P = 0.001).

CONCLUSIONeNO level varied between 10.72 ppb and 13.80 ppb in normal children 11 - 18 years of age, and was positively associated with age and height, but not with gender. eNO level increased significantly in children with wheezing and atopy.