Stability of blood eosinophils during acute exacerbations in patients with chronic obstructive pulmonary disease

Blood eosinophils are recommended by GOLD as a biomarker for inhaled corticosteroid (ICS) therapy in COPD, yet their stability during acute exacerbations of COPD (AECOPD) remains uncertain.

We retrospectively analyzed 3,311 hospitalized AECOPD patients (2018-2023). Blood eosinophil distribution, longitudinal trends, and within-patient variability were assessed. Linear mixed-effects models estimated overall trajectories of ln(1 + EOS) over standardized hospital days (SHD). Variability was quantified by coefficient of variation (CV%), within-patient SD (wSD), and median absolute change between consecutive tests. Robustness of thresholds (100 and 300 cells/µL) was examined by crossing and reclassification rates, with simulations of 20-30% overall decline. Near-threshold "decision bands" were derived from the empirical median change (≈ 50 cells/µL).

Blood eosinophils showed a right-skewed distribution with a median of 100 cells/µL (IQR 20-200). Mixed-effects models indicated only a mild overall increase (+ 2.16% per + 1 SD in SHD). In patients with repeated tests (n = 1,548), within-patient variability was substantial (median CV% 76.6%; wSD 57 cells/µL; median |Δ| 50 cells/µL). Threshold crossing and first-last reclassification were frequent (≥ 100: 45.7% and 32.9%; ≥300: 22.7% and 16.0%), and declined only slightly in simulated steroid-reduction scenarios. Approximately 13% of patients fluctuated between < 100 and ≥ 300 cells/µL during one admission.

EOS should be interpreted dynamically, with retesting or trend assessment recommended to guide clinical decisions during acute exacerbations.