Study highlights short-term within-day variation in blood eosinophils in patients with COPD

A new study quantified significant short-term within-day variability in blood eosinophil counts in patients with stable COPD.

“In COPD patients, long-term blood eosinophil count variability over several years has been documented. It has also been suggested that blood eosinophil count variability could be minimized by measurement at the same time of day, based on within-day blood eosinophil count variability data in asthma patients and normal subjects,” Inès Van Rossem, MD, with the faculty of medicine and pharmacy in the department of family medicine and chronic care at the Free University of Brussels, and colleagues wrote in the American Journal of Respiratory and Critical Care Medicine. “The study of blood eosinophil count variability in COPD has been identified as one of the main knowledge gaps that impedes its adoption into the routine of COPD patient management.”

Researchers recruited 50 outpatients with physician-diagnosed and spirometry-confirmed COPD (mean age, 69 years; 64% men) from March 2019 to January 2020. All patients had spirometry performed at 8 a.m. and blood samples collected at 8 a.m., 12 p.m. and 4 p.m.

Based on blood eosinophil counts at 8 a.m., three patients (6%) had a count of less than 100 cells/µL, 29 (58%) 100 cells/µL to 300 cells/µL and 18 (36%) 300 cells/µL or more. Median blood eosinophil count at 8 a.m. was 236 cells/µL, at 12 p.m. was 134 cells/µL and at 4 p.m. was 169 cells/µL.

Throughout the day, 50% of patients moved across at least one Global Initiative for Chronic Obstructive Lung Disease (GOLD) threshold and one patient moved across both thresholds.

The researchers reported significant differences between all three time points of blood sample collection, with a median change of –36%, or a decrease of 79 cells/µL, at 12 p.m. and –29%, or a decrease of 58 cells/µL, at 4 p.m. compared with measurements at 8 a.m. Compared with blood eosinophil counts measured at 12 p.m., counts measured at 4 p.m. showed a median change of 19%, or an increase of 18 cells/µL, according to the results.

The effect of time of day on blood eosinophil count remained significant when researchers only considered patients currently on inhaled corticosteroid therapy (n = 21) or patients with one or more moderate to severe COPD exacerbation in the past year (n = 24). When including only patients on inhaled corticosteroids (n = 29), median blood eosinophil count change was –43% at 12 p.m. and –29% at 4 p.m.

“Ideally, blood eosinophil count could be improved as a theragnostic biomarker by reaching a consensus on the time of day of blood sampling,” the researchers wrote. “This may not be workable in the reality of the clinic, in which case at least same time of day should be considered for the follow-up of any given patient.”