Variability in Blood Eosinophil Counts in Patients with Eosinophilic Asthma

Blood eosinophil (EOS) counts are critical to the accurate identification of asthma phenotypes. However, there are few long-term data on intraindividual EOS count variability among patients with eosinophilic asthma.

This post hoc analysis of 2 phase III clinical trials from the reslizumab BREATH program explored the variability of blood EOS counts in patients with eosinophilic asthma receiving placebo.

Pooled data from study participants receiving placebo (previously randomized 1:1 to receive reslizumab or placebo) were analyzed for blood EOS count variability over 52 weeks. EOS counts were measured up to twice during screening, every 4 weeks from randomization to the end of treatment and at the 90-day follow-up visit.

Of 476 included patients, 31 (6.5%), 38 (8.0%), 55 (11.6%), and 352 (73.9%) patients had baseline blood EOS counts of <150, ≥150 to <300, ≥300 to <400, and ≥400 cells/μL, respectively. Patients frequently shifted between EOS count categories during the 52-week treatment period, most often moving to the highest EOS category. Among patients in each of the lower 3 EOS categories, 27% to 56% of patients shifted to the ≥400 cells/μL category at some point during the treatment period.

Intraindividual variability in blood EOS count was high among patients with eosinophilic asthma receiving placebo, with shifts to ≥400 cells/μL from lower categories frequently observed. Repeat determinations of blood EOS count may be important to ensure appropriate selection of therapy in patients with severe asthma.