ABSTRACT
BACKGROUND/AIMS: Exhaled nitric oxide (NO) has been extensively investigated as a marker of airway inflammation in asthma, and fractional exhaled nitric oxide (FeNO) is recognized as a useful tool for its evaluation. The aim of this study was to investigate the relationships between FeNO levels and bronchodilator response (BDR), and between FeNO and mannitol-induced airway hyperresponsiveness (AHR), in patients with suspected asthma. METHODS: Clinical variables were collected from patients aged ≥ 13 years with suspected bronchial asthma and measured levels of FeNO. These levels were compared with patient values for forced expiratory volume in the first second (FEV1) and forced expiratory flow at 25 and 75% of the pulmonary volume (FEF(25-75%)) in bronchodilator response tests under control conditions, and during bronchial provocation with mannitol. Correlations and receiver operating characteristic (ROC) curves between FeNO levels and each test were assessed. RESULTS: A total of 259 patients were included in the analysis. The mean ages of the two test groups were 41.1 and 47.8 years, respectively. FeNO levels were strongly correlated with bronchodilator response (%) and with the mannitol dose producing a 15% fall in FEV1 (PD15). On the other hand, FeNO levels were only weakly correlated with FEF(25-75%). The optimal cut-off values for FeNO to predict a positive BDR and AHR were 38.5 and 29.5 parts per billion, respectively. CONCLUSIONS: This study suggests that FEV1 and FEF(25-75%) airway responses correlate with FeNO levels in patients with suspected bronchial asthma. FeNO levels may help to predict positive responses to BDR and AHR.