Eosinopenia in bronchiectasis: A novel biomarker for morbidity and mortality

Background: The paradigm of bronchiectasis is shifting away from its exclusive characterization as a neutrophilic condition. Patients with bronchiectasis and high eosinophil levels have been found to have a specific phenotype, but the clinical effect of eosinopenia remains unclear. Method: A retrospective, single-center, observational study was conducted at a tertiary medical center. Adult patients under follow-up for bronchiectasis from January 2007 to August 2020 were categorized by blood eosinophil count (BEC) as follows: eosinopenia (<100 cells/µL), normal (100-299 cells/µL), and eosinophilia (≥300 cells/µL). Data on the first hospitalization due to exacerbation and the community exacerbation rate in the first year of follow-up were analyzed. Mortality rates were assessed up to the end of follow-up on September 1, 2023. Results: The cohort included 724 patients (100%), 61% female (n = 442), of mean age 61 ± 16 years. The median follow-up period was 7.5 years (IQR: 5.1–10.8). Eosinopenia was found in 14.7% (n = 107), normal BEC in 56.6% (n = 417), and eosinophilia in 28.7% (n = 200). Patients with eosinopenia had a higher hazard ratio for first hospitalization than the normal-count group (1.71, 95% CI 1.11–2.64, p =.01) and the highest mean exacerbation rate (p =.04). On multivariate analysis, eosinopenia was significantly associated with higher mortality (HR 2.15, 95% CI 1.42–3.24, p <.001) after adjusting for age and sex. Conclusion: Eosinopenia in bronchiectasis emerged as a potential biomarker for adverse outcomes. Further study of its role in disease behavior may provide insights for the development of therapeutic strategies.