Measurement of Exhaled Nitric Oxide

Nitric oxide (NO) is an endogenous reactive molecule that is synthesised from the oxidative conversion of L-Arginine to L-Citrulline by the enzyme nitric oxide synthase (NOS). The upregulation of NOS in the airways occurs in response to proinflammatory cytokines through a variety of cellular mechanisms. Thus, exhaled NO is significantly increased in patients suffering from inflammatory airway diseases, especially in asthma. Moreover, exhaled NO measurement can also be used in COPD, differential diagnosis of chronic cough, sarcoidosis, and bronchiectasis. Currently, standardised guidelines and task forces are published for the techniques to measure exhaled NO. Chemiluminescence and electrochemical analysers are used to measure exhaled NO. In this review, the technical details of standardised NO measurements and factors affecting NO analysis, are discussed.