The levels and correlations of FeNO, blood eosinophils and lung function in well-controlled asthma

Introduction: Whether biomarkers (i.e., fractional exhaled nitric oxide (FeNO) and blood eosinophils) or lung function are additional ultimate outcomes in asthma treatment among patients with clinical remission has been the subject of previous research, the study of the correlations between FeNO, blood eosinophils and lung function among well-controlled asthmatic patients is less clear. To investigate the clinical application of the correlation between FeNO, blood eosinophils and lung function parameters in well-controlled asthmatic patients. Material and methods: This was a prospective cross-sectional study. We measured FeNO, blood eosinophil and lung function in 84 asthmatic patients with clinical remission who were assessed by asthma control questionnaires. The correlation coefficient was used to ascertain among those parameters. The diagnostic accuracy of blood eosinophil to identify low FeNO (< 25 ppb) was calculated using the area under the receiver operating characteristics (AUROC). Results: Of 84 patients analyzed, the median ACT was 25 and the median ACQ-7 was 0.43. The median duration of being well-controlled asthma was 14.5 months. The median FeNo was 23 ppb and the median blood eosinophils was 375 cell/mm(3). A significant positive correlation was found between FeNo and blood eosinophil (r = 0.310, p = 0.004). No correlation was detected between either FeNO or blood eosinophil and all lung function parameters. The AUROC results for blood eosinophils was 64.4% (p = 0.024) to detect FeNO < 25 ppb at a cutoff point of 295 cell/mm3 (sensitivity = 83.5%, specificity = 50%). Conclusions: Measuring FeNO and blood eosinophils in patients with a clinical remission of asthma may determine which of those patients have achieved complete remission. As the level of blood eosinophils has a significant correlation with FeNO, it may easily be a feasible biomarker to evaluate inactive airway inflammation before stepping down asthma treatment.