Abstract
BACKGROUND: High blood or sputum eosinophil counts are linked to poor clinical outcomes in chronic obstructive pulmonary disease (COPD), yet the value of combining both for the assessment of clinical prognosis remains unclear. In this study, we explore the value of combined blood and sputum eosinophil counts for assessing COPD outcomes. METHODS: Patients were divided into four groups by blood (≥300 cells/µL) and sputum (≥3%) eosinophil counts (low blood and low sputum, low blood and high sputum, high blood and low sputum, high blood and high sputum). Spirometry, questionnaires, CT scans, impulse oscillometry, blood laboratory tests and induced sputum tests were performed at baseline. Spirometry and follow-up questionnaires were performed annually. Poisson regression was used to compute the relative risk (RR) for acute exacerbation. The mixed-effects model was used to assess annual lung function decline. RESULTS: Compared with the low blood and low sputum eosinophils group, the high blood and high sputum eosinophils group had poorer lung function, more severe airway resistance and worse emphysema and air trapping at baseline. The high blood and high sputum eosinophils group had higher risks of cough (adjusted OR=1.87, 95% CI 1.20 to 2.92, p=0.006) and wheezing (adjusted OR=2.19, 95% CI 1.32 to 3.64, p=0.002). The low blood and high sputum eosinophils group had higher risks of phlegm (adjusted OR=1.53, 95% CI 1.04 to 2.24, p=0.029) and dyspnoea (adjusted OR=1.68, 95% CI 1.13 to 2.50, p=0.010). The high blood and high sputum eosinophils group demonstrated higher total (adjusted RR=1.36, 95% CI 1.15 to 1.60, p<0.001) and moderate-to-severe (adjusted RR=1.42, 95% CI 1.14 to 1.76, p=0.001) exacerbation risks. There was no significant difference in annual lung function decline among the groups. CONCLUSION: Elevated blood and sputum eosinophil counts are linked to worse lung function and a higher exacerbation risk in patients with COPD.