The relationship of fractional exhaled nitric oxide level with exercise-induced bronchoconstriction in Asian asthmatic children: A local single-centre retrospective diagnostic study

Background and Aims: Exercise-induced bronchoconstriction (EIB) is associated with eosinophilic inflammation of the airway in asthmatic children and studies showed fractional exhaled nitric oxide (FeNO) is associated with it. The aim of this study was to explore the relationship between FeNO and EIB and find a cutoff reference of FeNO for EIB based on existing normative data from healthy Asian children by Yao et al. in 2012. Materials and Methods: Asian asthmatic children who had undergone FeNO and exercise challenge test from January 1, 2016 to December 31, 2019 in a local respiratory centre were reviewed retrospectively. The FeNO values of the individuals were converted to z-score with reference to the predicted value of FeNO in Asian children by Yao et al. in 2012. A receiver-operating characteristic (ROC) curve is plotted to identify a cutoff representing EIB. Results: Data of 88 Asian asthmatic children aged 5–18 were retrieved. There is a significant overlapping of the FeNO z-scores of normal and mild EIB groups. The cutoff value determined by the Youden index (0.724) to predict moderate or severe EIB in asthmatic patients is 3.276 with sensitivity of 88.9% and specificity of 83.5%Conclusion: High FeNO value of z-score 3.276 has high sensitivity and specificity to moderate to severe EIB in Asian asthmatic children. FeNO could be used as a simple test in clinic setting before exercise challenge test is available.