Higher blood eosinophil counts in patients with chronic obstructive pulmonary disease are associated with less bronchial thickening and better lung function in a retrospective observational study published in BMJ Open. The findings suggest that quantitative computed tomography phenotypes may complement eosinophil-based risk stratification.

The researchers examined the association between eosinophil levels and computed tomography (CT) imaging by quantitatively assessing bronchial wall thickening, emphysema index, and pulmonary vascular parameters in patients with chronic obstructive pulmonary disease (COPD), stratified by blood eosinophil percentage and absolute eosinophil counts.

Patients with eosinophil levels of at least 2%, 150/µL, or 300/µL were observed to experience the benefits described above. Notably, in those with counts of at least 300/µL, the researchers reported that the emphysema index (EI) of the right upper lobe was reduced.

“These findings provide valuable insights into the role of [eosinophils] in COPD pathophysiology,” they wrote.

Study Population and Eosinophil Stratification

A total of 448 patients from a tertiary hospital in China who were diagnosed with COPD were included in the analysis. The cohort was mostly men (83%) with a mean age of 68.8 years and were classified as follows:

• By eosinophil percentage: 41% (184 cases) had levels greater than or equal to 2%.

• By absolute eosinophil count: 34% (151 cases) had counts greater than or equal to 150/µL.

• Further stratification: 9% (42 cases) had counts greater than or equal to 300/µL.

Lower eosinophil levels (defined as less than 2% or less than 150/µL) were found to be associated with a higher prevalence of chronic pulmonary heart disease. Neutrophil counts and percentages were higher in patients with lower eosinophils, including those with less than 2%, less than 150/µL, or less than 100/µL.

How Lungs Were Affected

When stratified by eosinophil thresholds of 2% and 150/µL, no statistically significant differences were observed in the entire lung, left lung, right lung, lung lobe volume, EI, and lung emphysema heterogeneity index. However, compared with patients with an absolute count of 100 to 300/µL, those with at least 300/µL had a lower EI of the right upper lobe of the lung.

Airway wall thickness, wall area percentage, and Pi10 (a standardized airway wall metric) were lower  when comparing higher vs lower eosinophil strata across multiple thresholds. In addition, Pi10 was lower in patients with counts of at least 300/µL compared with those with less than 100/µL.

Across different threshold values, including both percentage and absolute eosinophil counts, pulmonary vascular measurements—such as vessels with a cross-sectional area smaller than 5 mm², total blood volume, the ratio of small vessel volume to total blood volume, network length, branch points, and end points—showed no statistically significant differences.

Lung Performance

The percent predicted diffusing capacity for carbon monoxide was higher in patients with eosinophil levels of at least vs less than 2%. Patients whose blood eosinophil count was at least vs less than 150/µL had lower residual volume and lower residual volume to total lung capacity, along with higher percent predicted forced vital capacity and diffusing capacity.

At the threshold of at least 300/µL, multiple lung function measures were higher compared with patients with eosinophil counts below 100/µL or between 100 and 300/µL, including:

• Percent predicted forced expiratory volume in 1 second

• Maximal expiratory flow at 75%, 50%, and 25% of lung volume

• Percent predicted diffusing capacity for carbon monoxide.

Insights and Opportunities

The researchers reported several limitations of the study, including the single-center design, relatively small sample size, cross-sectional nature of the analysis, and software constraints that limited incorporation of additional quantitative CT indices.

“We highlight that the relatively high [eosinophil] levels were associated with mild airflow restriction, mild diffusion function limitation, and less bronchial thickening,” they concluded. “Besides, when the [eosinophil level] was [at least] 300/µL, the EI decreased significantly, especially in the right upper lobe, which indicates that QCT [quantitative CT] is useful in addressing the heterogeneity of eosinophilic COPD.”

As blood eosinophils increasingly inform inhaled corticosteroid decisions in COPD, the findings suggest that quantitative CT phenotyping may provide additional context for interpreting eosinophil strata within a broader treatable-traits framework.

Disclosure: The researchers reported no conflicts of interest.

Source: BMJ Open