The Role of Peripheral Eosinophil Counts in Identifying COPD Subtype

Elevated peripheral eosinophil counts may be a useful indicator for identifying patients with chronic obstructive pulmonary disease (COPD) and eosinophilic inflammation, irrespective of asthma history, according to research findings published in the journal Thorax.

Researchers sought to determine the prevalence of eosinophilic inflammation among individuals with COPD by analyzing elevated fractional exhaled nitric oxide (FeNO) levels and peripheral eosinophil counts. The analysis was based on National Health and Nutrition Examination Survey data from 2007 to 2010 for 3,110,617 patients (mean age, 59.3 years; 64.4% male) with COPD. All patients were age 40 or older and had a postbronchodilator forced expiratory volume in 1 second/forced vital capacity (FEV1/FVC) ratio less than 0.70.

Within the entire COPD cohort, 14.6% of patients had a history of asthma. The prevalence of asthma (vs no asthma) was highest among women (58.3% vs 31.7%, respectively; P <.001) and among those who were non-Hispanic and Black (6.2% vs 4.4%; P <.001) or non-White, non-Hispanic individuals of other races/ethnicities (11.4% vs 5.4%; P <.001).

While the overall prevalence of peripheral eosinophilia was 36%, the prevalence was significantly higher among patients with COPD and an asthma history vs. those with COPD and no asthma history (38.3% vs 35.5%; P <.001). Additionally, while 14.3% of the entire cohort had an elevated FeNO (of ≥25 ppb), elevated FeNO was higher among patients who had COPD and an asthma history (28.7%), compared with those who had COPD but no asthma history (15.2%).

In distinguishing patients with COPD and FeNO levels of at least 25 ppb from patients with FeNO levels less than 25 ppb, the researchers found that the sensitivities of peripheral eosinophil count thresholds of 100 cells/μL, 200 cells/μL, and 300 cells/μL were 90%, 50% and 33%, respectively, while specificities were 40%, 72%, and 90% (area under the curve, 0.70; 95% CI, 0.61-0.80).

A limitation of the study, researchers noted, was the fact that the NHANES data used were subject to both sampling and non-sampling errors, and that the asthma self-reports used were subject to recall bias.

The researchers concluded, “Elevated peripheral eosinophil counts have a good sensitivity and specificity in identifying COPD subjects with eosinophilic inflammation with or without a reported history of asthma.”

Reference

Annangi S, Nutalapati S, Sturgill J, Flenaugh E, Foreman M. Eosinophilia and fractional exhaled nitric oxide levels in chronic obstructive lung disease. Thorax. Published online August 20, 2021. doi:10.1136/thoraxjnl-2020-214644