Reference values and determinants of fractional concentration of exhaled nitric oxide in healthy children

Measurement of the fractional concentration of exhaled nitric oxide (FeNO) is a quantitative, noninvasive, simple, safe method of assessing airway inflammation. While FeNO measurement has been standardized, reference values for elementary school children are scarce. The aim of this study was to establish reference values for FeNO in children. FeNO was measured in elementary school children at 6-12 years of age in Seoul, Korea, following American Thoracic Society guidelines and using a chemiluminescence analyzer (NIOX Exhaled Nitric Oxide Monitoring System, Aerocrine, Sweden). A total of 1,252 children completed a modified International Study of Asthma and Allergy in Children (ISAAC) questionnaire; FeNO was measured in 1,063 children according to the protocol and in 808 children defined as healthy controls. Mean FeNO were 10.32 ppb, 16.58 ppb, and 12.36 ppb in non-atopic, atopic, and all 808 healthy controls, respectively. FeNO was not associated with age and gender. The FeNO reference equations were determined by multiple linear regression analysis, taking into account the variables of age, height, weight, total IgE, eosinophil percent, and bronchial hyper-responsiveness (methacholine PC20). FeNO=0.776+0.003×total IgE+0.340×eosinophil percent; coefficient of determination (R2)=0.084 in the 501 healthy non-atopic controls. FeNO=-18.365+1.536×eosinophil percent, R2=0.183 in the 307 healthy atopic controls; and FeNO=-7.888+0.130×Height+0.004×total IgE+1.233×eosinophil percent, R2=0.209 in the 808 all healthy controls. Eosinophil percent was correlated with FeNO in all healthy controls. FeNO was not associated with BMI. This study provides reference values for FeNO that can be used to evaluate airway inflammation in elementary school children. Determinants that could most accurately predict FeNO in healthy school-age children were assessed.