Relationship of exhaled nitric oxide to clinical and inflammatory markers of persistent asthma in children

Background: Exhaled nitric oxide (eNO) is a noninvasive test that measures airway inflammation. Insufficient information is available concerning correlations between eNO and biologic, physiologic, and clinical characteristics of asthma in children currently not taking controller medications. Objective: The aim of this study was to rind correlations between eNO and other characteristics of children with mild to moderate asthma currently not taking medications. Methods: Children aged 6 to 17 years with mild to moderate persistent asthma, taking only albuterol as needed, were characterized during 2 visits 1 week apart before being randomly assigned into a clinical trial. At the screening visit, online measurements of eNO, spirometry before and after bronchodilator, and biomarkers of peripheral blood eosinophils, serum eosinophil cationic protein, total serum IgE, and urinary leukotriene E-4 were obtained. During a week characterization period before randomization, symptoms were recorded on a diary and peak expiratory flows were measured twice daily using an electronic device. At the randomization visit, eNO was repeated followed by a methacholine challenge and aeroallergen skin testing. Correlations and rank regression analyses between eNO and clinical characteristics, pulmonary function, and biomarkers were evaluated. Results: eNO was significantly correlated with peripheral blood eosinophils (r = .51, P < .0001), IgE (r = .48, P < .0001), and serum eosinophil cationic protein (r = .31, P = .0003) but not with urinary leukotriene E4 (r = .16, P = .08). A moderate correlation was found between eNO and the number of positive aeroallergen skin tests (r = .45, P < .0001). eNO did not correlate with FEV1 % predicted but was weakly correlated with FEV1/forced vital capacity (r = -.19, P = .032), bronchodilator response (r = .20, P = .023), and FEV1 PC20 methacholine (r = -.31, P = .0005). No significant correlations were found between eNO and clinical characteristics or morning or evening peak expiratory flow measurements. The rank regression analysis demonstrated that 5 variables accounted for an R square of .52 (eosinophils [P < .0001], IgE [P = .0023]age [P < .0001], months of inhaled corticosteroid use in the year before study entry [P = .01], and FEV1 PC20 [P = .0061]). Conclusions: These findings suggest that eNO provides information about the asthmatic state consistent with information from other markers of inflammation. It is a noninvasive technique that could be used in decisional management of children with asthma.