Persistent and unstable eosinophil levels in the sputum and blood: impact on the clinical prognosis of patients with chronic obstructive pulmonary disease.

BACKGROUND

Patients with chronic obstructive pulmonary disease (COPD) with eosinophilia exhibit poor lung function. However, the prognostic impact of eosinophilia remains unclear. This study evaluates the relationship between sputum and blood eosinophil variability and the long-term clinical outcomes of COPD.

METHODS

Sputum eosinophil proportion ≥3% and blood eosinophil count ≥300 cells/µL were considered high. Based on sputum/blood eosinophil levels at baseline and at the 3-year follow-up, patients with COPD were divided into the persistently low, unstable, and persistently high sputum/blood eosinophils groups. Poisson regression was used to assess acute exacerbation risk, and mixed-effects models were used to evaluate lung function decline.

RESULTS

Compared with the persistently low sputum eosinophils group (n=183), the persistently high sputum eosinophils group (n=68) had more dyspnea and had a higher modified Medical Research Council score, poorer baseline lung function, and experienced more total exacerbations [adjusted relative risk (RR) 1.47, 95% confidence interval (CI): 1.21-1.80, P<0.001] and more moderate-to-severe exacerbations [adjusted RR 1.62, 95% CI: 1.25-2.10, P<0.001]. The unstable sputum eosinophils group (n=122) experienced more total exacerbations (adjusted RR 1.47, 95% CI: 1.24-1.75, P<0.001) and more moderate-to-severe exacerbations (adjusted RR 1.29, 95% CI: 1.02-1.63, P=0.03). Similarly, the persistently high blood eosinophils group experienced more total exacerbations than the persistently low blood eosinophils group (adjusted RR 1.27, 95% CI: 1.05-1.54, P=0.02), the unstable blood eosinophils group experienced more total exacerbations (adjusted RR 1.27, 95% CI: 1.07-1.51, P=0.008) and more moderate-to-severe exacerbations (adjusted RR 1.29, 95% CI: 1.03-1.62, P=0.03). There were no significant differences in lung function decline.

CONCLUSIONS

Persistent eosinophil elevation was associated with a higher exacerbation risk.