Association of Upon-Diagnosis Blood Eosinophilic Count with Frequency and Severity of Annual Exacerbation in Chronic Obstructive Pulmonary Disease: A Prospective Longitudinal Analysis

INTRODUCTION: There is a controversy regarding the relationship between blood eosinophil count and COPD exacerbation. We aimed to determine whether peripheral eosinophils upon COPD diagnosis could affect the frequency and severity of annual acute exacerbation of COPD (AECOPD). METHODS: This prospective study was conducted on 973 newly diagnosed COPD patients who were under 1-year follow-up in a pulmonology center in Iran. The Cox proportional model, polynomial regression, and receiver operator characteristic curves were conducted to evaluate the impact of the eosinophil levels on AECOPD. A linear regression model was conducted to evaluate the continuous association of eosinophilic count with AECOPDs. RESULTS: Patients with eosinophil >200 cells/microliter were higher pack-year smokers with more pulmonary hypertension prevalence compared to COPD patients with <200 cells/microliter. There was a positive correlation between the eosinophilic count and the frequency of AECOPDs. Eosinophil >900 cells/microliter and eosinophil >600 cells/microliter had a sensitivity of 71.1% and 64.3%, respectively, in predicting the occurrence of more than one AECOPD. Eosinophilic count cutoff of 800 cells/microliter had the highest Youden index with sensitivity and specificity of 80.2% and 76.6%, respectively, for incident AECOPD in newly diagnosed patients. Using a linear model, increasing 180 cells/microliter in serum eosinophils was associated with further exacerbation. Evaluating gender, BMI, smoking pack-year, FEV1/FVC, CAT score, GOLD score, pulmonary hypertension, annual influenza, pneumococcal vaccinations, leukocytosis, and blood eosinophils, only blood eosinophils (hazard ratio (HR) = 1.44; 95% confidence interval = 1.33–2.15; p value = 0.03) and GOLD score (HR = 1.19; 95% CI = 1.30–1.52; p value = 0.03) were found as independent risk factors of AECOPD >3 episodes/year. Requirement for ICU admission, invasive ventilation, and mortality rate due to AECOPDs was similar between eosinophilic and noneosinophilic groups. CONCLUSION: Eosinophilia upon COPD diagnosis is a factor of recurrent AECOPDs. To reduce the risk of AECOPDs and the burden of disease, clinicians may consider inhaler corticosteroids and domiciliary oxygen with a lower threshold for eosinophilic-COPD patients regardless of their clinical status.