Predictors of Low and High Exhaled Nitric Oxide Values in Asthma: A Real-World Study

<b><i>Background:</i></b> In asthma, exhaled nitric oxide (F_ENO) is a clinically established biomarker of airway T2 inflammation and an indicator for anti-inflammatory therapy. <b><i>Objectives:</i></b> The aim of the study was to identify, in an observational real-world cross-sectional study, the main characteristics of patients with asthma as classified by their F_ENO level. <b><i>Method:</i></b> We stratified 398 patients with stable mild-to-severe asthma according to F_ENO level as low (≤25 ppb) versus elevated (&#x3e;25 ppb), subdividing the latter into two subgroups: moderately elevated (26–50 ppb) versus very high F_ENO (&#x3e;50 ppb). Clinical, functional, and blood parameters were extrapolated from patients’ chart data and compared with the F_ENO stratification. Predictors of low and elevated F_ENO asthma were detected by logistic regression model. <b><i>Results:</i></b> Low BMI, higher blood eosinophilia, allergen poly-sensitization, the severest airflow obstruction (FEV₁/FVC), and anti-leukotriene use are predictors of elevated F_ENO values in asthma, as well as persistent rhinitis and chronic rhinosinusitis with or without nasal polyps. Beyond these, younger age, more than 2 asthma exacerbations/year, higher airflow reversibility (post-bronchodilator ∆FEV₁), and oral corticosteroid dependence are predictors of very high F_ENO values. In contrast, obesity, obstructive sleep apnoea syndrome, gastroesophageal reflux disease, arterial hypertension, and myocardial infarction are predictors of low F_ENO asthma. In our population, F_ENO correlated with blood eosinophils, airflow obstruction, and reversibility and negatively correlated with age and BMI. <b><i>Conclusions:</i></b> Stratifying patients by F_ENO level can identify specific asthma phenotypes with distinct clinical features and predictors useful in clinical practice to tailor treatment and improve asthmatic patients’ outcomes.