A pathophysiological approach for FeNO: A biomarker for asthma.

The present review is focused on literature concerning the relevance of fractional exhaled nitric oxide (FeNO) in clinical practice from a pathophysiological point of view. There is increasing evidence that asthma is a heterogeneous pathological condition characterised by different phenotypes/endotypes related to specific biomarkers, including FeNO, helpful to predict therapeutic response in selected asthmatic populations. Nowadays FeNO, a non-invasive biomarker, appears to be useful to foresee asthma developing, to recognise specific asthma phenotypes, like the eosinophilic, to ameliorate asthma diagnosis and management in selected populations and to predict standard corticosteroid and biologic therapy efficacy. In addition, FeNO assessment may also be useful in patients with allergic rhinitis in order to detect the potential involvement of eosinophilic bronchial inflammation in "case finding" subjects at risk of asthma diagnosis. Therefore, it is possible to hypothesise a future with an appropriate use of FeNO by physicians dealing with worrisome clinical issues in specific asthma phenotypes.