BACKGROUND
The Global Initiative for Chronic Obstructive Lung Disease (GOLD) report considers blood eosinophil counts <100 cells/μL (BEC≤100) in individuals with COPD (Chronic Obstructive Pulmonary Disease) to predict poor inhaled corticosteroid (ICS) responsiveness. However, the BEC≤100 phenotype is inadequately characterized, especially in advanced COPD.
RESEARCH QUESTION
Are there differences between GOLD Group D patients with high BEC and those with low BEC regarding baselines characteristic and longitudinal outcomes?
STUDY DESIGN AND METHODS
We used multivariable mixed models and logistic regression to contrast clinical characteristics and outcomes of BEC≤100 versus BEC>100 (BEC100+) in all COPD subjects (n=1414) and GOLD Group D (n=185) not on ICS.
RESULTS
We identified n=485 with BEC≤100 (n=61 Group D) and n=929 individuals with BEC100+ (n=124 Group D). BEC≤100 status was stable at 6 and approximately 52 weeks (intraclass correlation of 0.78 and 0.71, respectively). Compared to BEC100+, BEC≤100 comprised more women, with greater current smoking, and less frequent childhood asthma. Among all analyzed participants, the two BEC-defined subsets showed similar rates of lung function decline (mean slope, BEC≤100, -50 vs. -39 mL/year, P=0.140), exacerbations (0.41 vs. 0.36/year, P=0.098), subsequent ICS initiation (2.5% vs. 4.4%, P=0.071), and mortality (7.8% vs. 8.4%, P=0.715). However, in GOLD Group D, BEC≤100 individuals showed higher exacerbation rates within 365 days after enrollment (0.62 vs. 0.33/year, P=0.002) and total follow-up (1.16 vs. 0.83/year, P=0.014). They also had greater lung function decline (mean slope of -68 mL/y vs. -23 mL/y, P=0.036), and had greater emphysema at baseline (voxels below 950 Hounsfield units at total lung capacity of 7.46% vs. 4.61%, P=0.029).
INTERPRETATION
In non-ICS-treated GOLD Group D COPD, indviduals with BEC≤100 had more baseline emphysema, prospective exacerbations, and lung function decline. Our analysis identified a particularly vulnerable subpopulation of individuals with COPD, suggesting the need for studies focused specifically on their therapeutic management.