Blood Eosinophil Count, Disease Severity, and Exacerbation Risk in Korean Patients with Bronchiectasis: A Retrospective Cohort Study

BACKGROUND: Peripheral blood eosinophil count has been associated with bronchiectasis outcomes, but findings are inconsistent. Its role in acute exacerbations among Korean patients remain unclear. METHODS: This study retrospectively evaluated 492 patients with bronchiectasis at a tertiary hospital in Korea between 2014 and 2021. Using a negative binomial regression model adjusted for follow-up duration, we evaluated the association between peripheral eosinophil counts and acute exacerbations in Korean patients with bronchiectasis. RESULTS: Among the 492 patients, 190 (38.6%) were categorized into the lower eosinophilic group, 221 (44.9%) into the normal eosinophilic group, and 80 (16.2%) into the higher eosinophilic group. No significant differences were observed across eosinophilic groups in terms of hospitalization within one year, BSI scores, or FACED scores (all p > 0.05). In the parsimonious negative binomial regression analysis with false discovery rate (FDR) correction, oral corticosteroid use (IRR = 2.26; 95% CI: 1.46-3.52; FDR p = 0.001), older age (IRR = 1.03; 95% CI: 1.01-1.04; FDR p = 0.002), and lower FEV1 % predicted (IRR = 0.98; 95% CI: 0.97-0.99; FDR p < 0.001) were identified as independent risk factors for acute exacerbations. Conclusions: There was no significant association between peripheral blood eosinophil counts and either acute exacerbations or disease severity in Korean patients with bronchiectasis. In contrast, older age, lower lung function (FEV1 % predicted), and the use of oral corticosteroids were identified as independent risk factors for acute exacerbations. These findings underscore the importance of considering region-specific clinical and epidemiological factors in the management of bronchiectasis.