Clinical aspects of using exhaled NO in asthma diagnosis and management

Background Current guidelines recommend tailoring of asthma management according to disease control, which is largely defined by increased symptoms and deterioration in lung function. These features do not reflect the severity nor the type of the asthmatic airway inflammation. Fractional exhaled nitric oxide (FENO) is a simple, non-invasive and cost-effective online test applicable in both adults and children. In addition to symptoms and lung function measurements, FENO reflects airway eosinophilia and hence allows online assessment of the corticosteroid-sensitive T helper 2 type airway inflammation in asthmatic patients. FENO can thus be applied to aid asthma diagnosis and treatment monitoring both in clinical practice and for research purposes. Objectives The scope of this review is to provide an overview of the most important clinical studies using FENO in asthma management and to summarise the implications of FENO measurements in clinical practice. Results and Conclusion In several studies, FENO measurements provided additional information on aspects of asthma including phenotyping, corticosteroid-responsiveness and disease control. Thus, if correctly applied and interpreted, FENO can aid asthma diagnosis, identify patients at risk of exacerbation and support customized treatment decisions. A simple and reliable tool to quantify peripheral nitric oxide will further aid to identify patients with small airways inflammation.