The following is a summary of “Clinical Implications of Longitudinal Blood Eosinophil Counts in Patients With Severe Asthma,” published in the June 2023 issue of Allergy and Clinical Immunology by Bleecker et al.

Uncertainty surrounds the stability and variability of blood eosinophil counts (BECs) to phenotype patients with severe asthma. This post hoc, longitudinal, merged analysis of placebo-arm patients from two phase 3 studies assessed the clinical significance of BEC stability and variability in moderate-to-severe asthma. This analysis included patients from SIROCCO and CALIMA who received maintenance medium- to high-dose inhaled corticosteroids plus long-acting β2-agonists; patients with BECs of 300 cells/L or greater were enrolled in proportion to those with BECs of less than 300 cells/L. 

Over one year, the BECs were measured six times in a central laboratory. Exacerbations, lung function, and Asthma Control Questionnaire 6 scores were recorded for patients classified according to BEC (<300 cells/μL or  ≥300 cells/μL) and variability (<80% or ≥80% BEC less than or greater than 300 cells/μL). About 42.2% (n = 303) of 718 patients had mainly high BECs. In contrast, 30.9% (n = 222) had predominantly low BECs, and 26.9% (n = 193) had variable BECs. Prospective exacerbation rates (mean ± standard deviation) were significantly higher in patients with mainly high (1.39 ±2.20) and variable (1.41±  2.09) BECs compared to patients with predominantly low (1.05±  1.64) BECs. 

Identical outcomes were observed for the number of exacerbations in patients receiving a placebo. Although patients with variable BECs experienced intermittently high and low BECs, their exacerbation rates were comparable to those of the predominantly high BEC group, which were higher than those of the deficient BEC group. A high BEC supports an eosinophilic phenotype in clinical contexts without additional measurements, whereas a low BEC necessitates repeated measures because it may reflect intermittently high or predominantly low BECs.

Source: sciencedirect.com/science/article/pii/S2213219823002246