Spirometry‐adjusted fraction of exhaled nitric oxide increases accuracy for assessment of asthma control in children

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Exhaled nitric oxide (NO) has been used as non‐invasive, easy to measure, reproducible and immediately available biomarker of airway inflammation in allergic diseases.1 Standardized procedures for its measurement2 and clinical use3 have already been published, with a strong level of evidence in the diagnosis of eosinophilic airway inflammation and for monitoring airway inflammation in patients with asthma.3 In fact, the expression of inducible nitric oxide synthetase mRNA has been shown to be increased in the airways of subjects with asthma4 and to be downregulated by the use of inhaled steroids.5
Although the diagnostic accuracy of exhaled NO in the identification of asthma in children is moderate, it suggests that it might be a promising tool6 and the confounding or effect modification of atopy is believed to be a key feature that limits the usefulness of exhaled NO in asthma diagnosis.
Exhaled nitric oxide has shown to be efficient in guiding medication management, as a reduction of 20% in exhaled NO is considered indicative of a response to anti‐inflammatory therapy.3 However, no significant advantage was seen with the specific use of exhaled NO‐driven protocols to guide asthma treatment compared with other methods,7 and according to GINA guidelines,9 treatment of asthmatic children usually relies on symptoms reported by the child and/or guardians. Furthermore, correlations between airway inflammation and symptoms, asthma control and asthma severity are weak or absent.1 In steroid‐naïve patients, high exhaled NO levels predict a good response to inhaled corticosteroids (ICS) treatment, and a low level of exhaled NO in adults in ICS treatment is associated with reduced likelihood ratio of exacerbation.12 Until now, it is not possible to provide clear recommendations for the utility of the exhaled NO in asthma management, as studies failed to show an overall benefit in the rate of exacerbations as well as in asthma control, lung function and use of oral corticosteroids during exacerbations.13 In a recent study, exhaled NO was used in relation to FEV1 (exhaled NO/FEV1) to distinguish patients with asthma from those without with promising results.14 This kind of approach could be a way to minimize the influence of baseline bronchial constriction on exhaled NO.
With this study, we aimed to assess the ability of spirometry‐adjusted fraction of exhaled nitric oxide to identify and assess asthma control in children, in comparison with traditional approaches.

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