Further Research on Blood Eosinophil Count in COPD Needed, According to Review

A review published in Canadian Respiratory Journal states that blood eosinophil count (BEC) is a proposed biomarker that may indicate clinical outcomes in patients with chronic obstructive pulmonary disease (COPD). However, few studies have tracked the stability of BEC in predicting outcomes in patients with COPD.

This review aimed to enumerate several areas of research that have yielded varying conclusions on the stability of BEC in patients with COPD.

Inclusion criteria in studies “matter a great deal,” according to the authors. The inclusion of participants with a history of asthma has led to varying results, as “BEC can be abnormal in asthmatic patients.” Participants with a known history of asthma were excluded in some studies assessing stability of BEC but not in others.

Asthma-COPD overlap (ACO) is a disease with features of both COPD and asthma. Elevated BEC is listed as a diagnostic criteria of ACO, according to the Spanish Guidelines on the Management of Asthma. An increase in BEC levels could be a useful data point for indicating the possibility of ACO in patients already diagnosed with COPD. However, the decision to exclude patients with ACO from studies on BEC stability remains controversial, according to the authors.

The lack of standard criteria defining BEC stability makes it harder to interpret results across different studies, the review authors noted. “More scientific inquiries into BEC stability need to be further explored,” they wrote.

Next, they mentioned that differences in statistical analysis may influence study results. Varying methods of stratification can affect results, but even with the same strata, results may still differ. Across studies, patients’ measurements can be taken years or days apart. Many studies that used the intraclass correlation coefficient to estimate measurement repeatability produced results of fair to good (0.40-0.75) or excellent (>0.75) for BEC stability, according to the authors.

Different studies set different thresholds within their groups, which can lead to variability in the results. According to a study cited, the best cutoff depends on the correlation between the baseline and follow-up BEC. More exploration of BEC could help thresholds be more precise.

The authors noted the disagreement among studies in whether to exclude patients who use oral corticosteroid (OCS). One study cited in the review found that there was a reduction of BEC after OCS treatment, another found that OCS did not change BEC among patients with COPD, and a third found that OCS was associated with a reduction of BEC that returned to baseline after a wash-out period.

All of these results have duration of OCS use as a factor in the different results. The authors of this review proposed a wash-out period for patients who use OCS for future studies of OCS.

Similarly, smoking status is a factor with unknown contributions to BEC stability. One cited study found that nonsmoking patients with COPD and smoking patients with COPD had no difference in BEC counts, whereas another found that a current smoking habit was associated with higher BEC but former smoking and cumulative smoking exposure was not. The authors wrote that the underlying mechanisms of smoking in BEC stability need to be explored in more detail.

Other factors need to be taken into consideration, including race, ethnic differences, and the duration of follow-up in each study, the review authors noted. They would also like future research to further investigate the mechanisms and genetic impact on blood eosinophil levels in order to further discover the capacity of BEC as a biomarker of COPD.

The authors concluded that additional cohort studies with longitudinal tracing times and more frequent BEC measurements of patients with COPD are needed.

“With the mechanisms of BEC in COPD being further explored, it is hoped that BEC will better guide the clinical management of COPD patients in the future,” the authors wrote.

Reference

Cai CS, Wang J. Factors influencing the stability of blood eosinophils counts in chronic obstructive pulmonary disease patients. Can Respir J. 2022;2022:8369521. doi:10.1155/2022/8369521