Correlations of induced sputum eosinophils with blood allergic markers in pediatric asthma and eosinophilic bronchitis

Purpose: Induced sputum eosinophil count is useful for the evaluation and diagnosis of asthma and eosinophilic bronchitis (EB). The aim of this study was to evaluate the correlation of induced sputum eosinophil count with various allergic indicators, including the peripheral blood eosinophil count, in pediatric asthma and EB. Methods: From May 2014 to July 2018, 126 children visited Kyungpook National University Children's Hospital, and underwent methacholine bronchial challenge test and sputum induction. Peripheral blood eosinophil counts, serum eosinophil cationic protein (ECP), serum total IgE, immunoCAP for inhalant allergens, and skin prick test were performed in the study subjects. Results: In the asthma group, the eosinophil count of induced sputum correlated with peripheral blood eosinophils (r= 0.279, P= 0.043). The concordance rates of sputum and peripheral blood eosinophil count in the asthma and EB groups were 64.1% and 25.7%, respectively. The number of eosinophils in the sputum also correlated with serum total IgE, ECP, and specific IgE to Dermatophagoides farinae, Dermatophagoides pteronyssinus, and Aspergillus in the asthma group. Conclusion: The number of eosinophils in the induced sputum correlated with peripheral blood in the asthma group. However, a third of subjects were discordant. Therefore, we need to keep in mind the possibility of discordance when predicting the degree of airway eosinophilic inflammation using the peripheral blood eosinophils. In EB, the number of induced sputum eosinophils did not correlate with the number of peripheral blood eosinophils, which may be attributed to the difference in mechanism. Further studies are warranted.