Published online: November 15, 2017
Chronic obstructive pulmonary disease (COPD) is a major public health problem leading to high health care utilizations, poor health-related quality of life, and substantial cost burden and deaths worldwide. COPD affects approximately 10% of adults 40 years of age or older as determined by lung function testing, which is the best marker of the disease. Biomarker measurement in sputum and blood during acute COPD exacerbations identify four major phenotypic clusters of patients: bacterial (35%), viral (30%), eosinophilic (24%), and pauciinflammatory with minimal inflammatory changes (11%). Exacerbations represent a major and frequent burden for patients with COPD. The best predictor for frequent exacerbations is a prior COPD exacerbation. Other predictors reported include gastroesophageal reflux, poor health-related quality of life, and elevated white blood count. Given the finding that high blood eosinophil counts is predictive of future exacerbations in asthma, it was important to determine whether a similar relationship might exist in COPD, another obstructive pulmonary disease.
In a recent study published in The Journal of Allergy and Clinical Immunology: In Practice, Zeiger, et al. examined the relationship between blood eosinophil count to future COPD exacerbations in a cohort of COPD patients with both physician and post-bronchodilator FEV1/FVC diagnoses in a managed-care setting. The authors hypothesized that high blood eosinophil counts at baseline would be an independent risk factor for future exacerbations in COPD. Using administrative pharmacy and health care utilization data from 2009-2012, patients aged >40 years with a COPD diagnosis, post-bronchodilator FEV1/FVC <0.7, and a blood eosinophil count (N=7,245) were identified. COPD exacerbations were defined as hospitalizations or emergency department (ED) visits with a primary diagnosis of COPD, or outpatient visits with systemic corticosteroid dispensing within +14 days associated with an encounter code consistent with a COPD exacerbation. The relationship between the index blood eosinophil count and the rate of COPD exacerbations in the follow-up year was determined by multivariable analyses, adjusting for potential confounders.
COPD patients were predominantly male (57.1%), white (71.8%), often current or past smokers (75.4%), and had frequent comorbidities. 19.0% had eosinophil counts ≥300 cells/mm3, 76.1% were classified as moderate to very severe by lung function, and the COPD exacerbation rate was about 0.4 per year. After adjustment for potential confounders, COPD exacerbations during 1-year follow-up were significantly greater for patients with high blood eosinophil counts: ≥300 cells/mm3 (rate ratio (RR) 1.25, 95% CI 1.10-1.43), ≥400 cells/mm3 (RR 1.48, 95% CI 1.26-1.75), and ≥500 cells/mm3 (RR 1.76, 95% CI 1.45-2.14), respectively, compared with patients with eosinophils lower than the cutoffs.
In this study, high blood eosinophil counts were an independent risk factor for future exacerbations in COPD patients, a phenotype that might benefit from therapy directed at eosinophilic-driven disease and inflammation. To improve outcomes for COPD patients, population care management programs and clinical practices could consider measurement of blood eosinophils count to identify a phenotype with elevated blood eosinophils that are at risk for exacerbations and warrant closer monitoring or additional therapies.
The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.