MODERN APPROACHES TO FRACTIONAL EXHALED NITRIC OXIDE AS A USEFUL BIOMARKER FOR ALLERGIC ASTHMA PHENOTYPING AND MANAGEMENT.

Asthma is a pathologically heterogeneous disease, consisting of several phenotypes. Different types of airway inflammation are the cornerstone feature of this condition. Fraction of nitric oxide in exhaled air (FENO) has been proposed as a noninvasive, specific biomarker for eosinophilic airway inflammation and has been shown to be elevated in patients with allergic asthma phenotype. More recent studies indicate that FeNO identifies T-helper cell type 2 (Th2)-mediated airway inflammation with a high predictive value for identifying inhaled corticosteroid (ICS) responsive airway inflammation. Taking into account the accumulated evidence,it is possible to consider, that FeNO testing has an important role in the assessment of patients with suspected asthma and in the management of established asthmadiagnosis. In conjunction with symptom scores and lung function tests, FeNO measurement could provide a more useful and effective approach for asthma in terms of: (1) detecting the presence of Th2-mediated airway inflammation, (2) determining the likelihood of ICS responsive (and lack of course), (3) monitoring of airway inflammation to determine risk for future impairment or loss of asthma control during reduction/cessation of ICS treatment, (4) unmasking (otherwise unsuspected) non-adherence to corticosteroid therapy and (5) in severe asthma cases tailoring treatment with biological drugs. However, more work is still needed to address outstanding questions about its exact role in guiding asthma management and better define the use of FENO in different clinical settings.