Serial blood eosinophils and clinical outcome in patients with chronic obstructive pulmonary disease

BACKGROUND: Blood eosinophils have been suggested as a potential biomarker in chronic obstructive pulmonary disease (COPD), and their stability over time has been investigated in a few studies. However, the association between the stability of blood eosinophils and long-term clinical outcomes in COPD patients has yet to be fully elucidated. This study aimed to evaluate the stability of blood eosinophils and its association with clinical outcomes in COPD patients. METHODS: In total, 299 COPD patients from the Korean Obstructive Lung Disease cohort with at least two blood eosinophil measurements were included. Patients were stratified according to a cut-off of 300 cells/μL, and the association between eosinophil changes and all-cause mortality was analysed. The annual decline in forced expiratory volume in 1 s (FEV(1)), serial changes in St George’s Respiratory Questionnaire score (SGRQ), and exacerbations during follow-up were compared among eosinophil groups. RESULTS: Patients were stratified into three groups according to the blood eosinophil cut-off: persistently < 300 cells/μL (PL; n = 175), variable (V; n = 68), and persistently ≥300 cells/μL (PH; n = 56). There were no significant differences in baseline characteristics (age, sex, smoking, body mass index, use of inhaled corticosteroids, exacerbations in the previous year, FEV(1) (L or % predicted), or emphysema score) among the groups. During a median follow-up of 6.0 years, the PH group had a better survival rate than the PL group (adjusted mortality rate ratio, 0.29; 95% confidence interval, 0.09–0.97; P = 0.045). The PH group also showed improved symptoms and impact domains of SGRQ score compared to the PL group. No difference was found in annual FEV(1) decline or exacerbations during follow-up among the groups. CONCLUSIONS: Patients with persistently high blood eosinophils had a better survival rate than those with persistently low blood eosinophils. Serial follow-up of blood eosinophils could help to predict outcomes in COPD patients. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12931-018-0840-x) contains supplementary material, which is available to authorized users.