Review Raises Questions About the Role of Blood Eosinophils as a Biomarker in COPD

Using blood eosinophils as a proxy for tissue eosinophils has become a biomarker for the risk of exacerbation, as well as for response to inhaled corticosteroids, in patients with chronic obstructive pulmonary disease (COPD), and blood eosinophils are currently considered a treatable trait for managing COPD. However, a review published recently in the Journal of Clinical Medicine calls for a reassessment of the role of blood eosinophils in COPD.

The potential role of blood eosinophils in COPD has been based largely on data from post-hoc and retrospective analyses in large clinical trials that have not systematically excluded patient with asthma, according to the review. While these studies do support a relationship between blood eosinophils, exacerbations, and steroid response in COPD, the associations may not imply a pathological role of eosinophils in creating exacerbations.

Furthermore, there is no consensus about which level of blood eosinophils should be used to guide steroid therapy; data from studies into eosinophil levels have shown that in smokers with and without COPD and no history of asthma, blood eosinophil values are similar. Additionally, data have suggested that patients with COPD who have particularly high levels of blood eosinophils may have asthma. This fact is important, given that there is evidence that the function of eosinophils in COPD exacerbations differs from their function in asthma.

The authors also noted that blood eosinophils may have a paradoxical benefit for patients with COPD; in patients with blood eosinophil counts of 2% or greater versus patients with counts of less than 2%, improved pulmonary function, better quality of life, fewer symptoms, and fewer comorbidities have been reported. The risk of pneumonia—irrespective of use of inhaled steroids—has also been shown to be lower in patients with blood eosinophil counts of 2% or greater. These facts suggest, wrote the authors, that using therapies that target eosinophils may actually be harmful to patients with COPD.

According to the authors, future clinical trials that stratify patients according to their blood eosinophil counts and compare patients with COPD with and without histories of asthma could help to answer some key questions about the role of blood eosinophils as a biomarker for exacerbation risk and response to steroids in this challenging disease state.

Reference

Tine M, Biondini D, Semenzato U, et al. Reassessing the role of eosinophils as a biomarker in chronic obstructive pulmonary disease [published online July 2, 2019]. J Clin Med. doi: 10.3390/jcm8070962.