The measurement of exhaled nitric oxide in routine practice.

Exhaled nitric oxide (NO) is considered the most easily available clinical test to indirectly assess the level of eosinophilic airway inflammation in asthma, and to predict the efficacy of anti-inflammatory treatment with inhaled corticosteroids (ICS). It is possible to measure the level of exhaled NO using online or offline methods. The most widely used online method employs techniques that enable NO in exhaled air to be measured in a single exhalation, calculating the value at the end-expiratory plateau. Because of the correlation between the level of exhaled NO with the level of eosinophilic inflammation in the airway of asthmatic patients, it has been proposed as a clinical marker in the practice of respiratory and allergy physicians with differing targets. In particular it is considered to be highly effective in the diagnosis of allergic asthma, to be capable of identifying those patients with a higher response probability to inhaled corticosteroids, and to a lesser extent, to be of value in contributing to the management of the disease. The possibility of easily taking measurements of FeNO in an office setting even by relatively young children, and the availability of a portable device, opens a significant perspective for the routine use of FeNO evaluation in daily practice.