Reference ranges for induced sputum eosinophil counts in Korean adult population

BACKGROUND: Induced sputum analyses are widely utilized to evaluate airway inflammation in asthmatics. However, the values have not been examined in Korean adults. OBJECTIVE: The purpose of this study is to determine reference ranges for induced sputum eosinophils and their influencing factors in Korean adults. METHODS: A total of 208 healthy nonasthmatic adults were recruited. Sputum induction and processing followed the international standard protocols. RESULTS: Adequate sputum samples were successfully collected from 81 subjects (38.9%). The upper 90 percentile for sputum eosinophil was calculated as 3.5%. The median value of eosinophil count percentage was significantly higher in subjects with atopy than those without atopy (median, 1.6%; range, 0-11.0% vs. median, 0%; range 0-3.6%, p=0.030). However, no significant correlations were found with age, gender, body mass index, smoking status, blood eosinophil, or fractional exhaled nitric oxide levels. CONCLUSION: Current study was the first attempt to determine the reference ranges of induced sputum eosinophils in Korean adults. The cutoff value for sputum eosinophilia was 3.5%, and was significantly associated with atopy.