Low and High Blood Eosinophil Counts as Biomarkers in Hospitalized Acute Exacerbations of COPD

Background: Characterizing acute exacerbations of COPD (AECOPD) and individualizing therapy is challenging. Key exacerbation therapies include antibiotics and systemic corticosteroids. Blood eosinophils, when either low or high, may offer a simple, inexpensive distinction to predict beneficial responses to these therapies. Methods: We conducted derivation (n = 242) and validation (n = 99) cohort studies of patients hospitalized for AECOPD. Patients who received oral corticosteroids before ED presentation were excluded. The derivation cohort was identified by individual case file review. The validation cohort was prospectively recruited during hospital admission. Exacerbations were grouped according to blood eosinophil count as low (<50/μL), normal (50-150/μL), or high (>150/μL). Exacerbations were classified as being associated with infection if either virus testing was positive or C-reactive protein was ≥20 mg/L. Associations of eosinophil groups with infection, hospital length of stay, and 12-month survival were compared using appropriate statistical methods. Results: There were no significant differences in baseline characteristics between patients with low, normal, or high blood eosinophils in either cohort. Eosinophil counts <50/μL were more strongly associated with infection (91% vs 51.9%, P = .001), distinguished patients with longer median hospital stays (7 vs 4 days, P < .001), and were associated with lower 12-month survival (82.4% vs 90.7%, P = .028; pooled data of both cohorts) than eosinophil counts >150/μL. Conclusions: Low and high blood eosinophil counts in hospitalized patients with AECOPD provide a practical clinical distinction that can potentially be used to inform management strategies. Prospective studies are needed to evaluate if this strategy can guide discriminate use of antibiotics and/or corticosteroids.