Progress in the clinical application of fractional exhaled nitric oxide in diagnosis and treatment of bronchial asthma

Fractional exhaled nitric oxide （FeNO） is a biomarker of type 2 inflammation， and produced by nitric oxide synthase （NOS） expressed on the airway epithelial cells， with the substrates of <i>L</i>-arginine and oxygen. Type 2 cytokines such as interleukin （IL）-4 and IL-13 can up-regulate inducible NOS， which results in the abundant production of NO. NO plays an important role in the pathogenesis of bronchial asthma， and is closely associated with the airway inflammation and remodeling， reduction of lung function and eosinophil infiltration， etc. The technique of FeNO test is applied in the clinical diagnosis of asthma， predicting the response to steroids and evaluating the compliance of asthmatic patients. In recent years， it also plays a guiding role in choosing the optimal biologics for individual therapy for patients of asthma. As a non-invasive， convenient， and economical method， the role of FeNO in the diagnosis and treatment of asthma will be better understood and applied.