Assessment of the role of fractional exhaled nitric oxide as a predictor of airway eosinophilia and corticosteroid responsiveness in patients with chronic cough

Abstract Background Fractional exhaled nitric oxide (FeNO) can be used as a rapid indicator of eosinophilic airway inflammation and steroid responsiveness in patients with bronchial asthma, but this role in chronic cough is still questionable. So, this study was carried out to assess the role FeNO as a predictor of airway eosinophilia and inhaled steroids responsiveness in patients with chronic cough. This prospective study included 70 patients with undiagnosed chronic cough and 20 healthy non-smoker control group. Sputum eosinophils % and FeNO were measured before and after a 4-week treatment trial with high dose inhaled corticosteroids. The optimal cut-off value of FeNO to predict sputum eosinophilia and the responsiveness of cough for corticosteroids were determined. Results Forty-five patients (64.3%) of the studied 70 patients with chronic cough responded to the 4-week trial of inhaled steroids. In the steroid responder group, FeNO and sputum eosinophils % were significantly higher than in the non-responder group. There was a significant positive correlation between FeNO and sputum eosinophils %. The optimal cut-off value of FeNO to detect airway eosinophilia was 33 ppb (with 65% sensitivity and 80% specificity) The ROC AUC was 0.757 and the optimal cut-off value of FeNO to predict corticosteroids responsiveness was 34.5 ppb (with 85% sensitivity and 90% specificity). The ROC AUC was 0.835. Conclusion FeNO can be used as a rapid and non-invasive diagnostic tool of airway eosinophilic inflammation and as a predictor for steroid responsiveness in patients with chronic cough.