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Blood eosinophil counts fluctuate frequently in patients with eosinophilic asthma

Published online: March 1, 2021

Eosinophilic asthma is a type of severe asthma characterized by an increase in eosinophil (EOS) count. Eosinophilic asthma can have a great impact on a patient’s quality of life, and patients with eosinophilic asthma are at an increased risk of severe asthma exacerbations and tend to have impaired lung function and poor symptom control. Blood EOS counts are key to supporting the diagnosis and management of eosinophilic asthma; however, blood EOS counts in an individual patient can fluctuate greatly. This variability may have implications in both research and clinical practice, but few published long-term data exist on EOS variability in patients with eosinophilic asthma.

In a recent study published in The Journal of Allergy and Clinical Immunology: In Practice, Corren and colleagues investigated the variability of EOS count across several EOS count categories in patients who received placebo in randomized controlled trials. Results from 2 duplicate, 52-week phase III trials were pooled and analyzed on a post hoc basis. Eligible patients had at least 1 blood EOS count of ≥400 cells/μL during a 4-week screening period, after which they were randomized (1:1) to receive either reslizumab or a placebo every 4 weeks for 52 weeks. Blood EOS counts were measured during screening, at randomization (considered baseline), every 4 weeks from randomization until the end of the 52-week treatment period, and at a 90 day follow-up visit. Patients were categorized into four groups based on their baseline blood EOS count: <150 cells/µL, ≥150 to <300 cells/µL, ≥300 to <400 cells/µL and ≥400 cells/µL. Variability of blood EOS counts in each patient was then quantified by analyzing the proportion of patients staying in or shifting between categories. In addition, the authors assessed the differences between variability within individual patients, and the variability across the patient population.

The authors found that patients frequently shifted between EOS count categories during the 52-week treatment period. Patients with a baseline blood EOS count of ≥400 cells/μL were most likely to remain in this EOS category. Among patients in each of the lower three EOS categories, 27% to 56% of patients shifted to the ≥400 cells/µL category at some point during the treatment period. Patients with baseline counts of <400 cells/μL demonstrated a high proportion of shifts to the highest category, from one visit to the next. The authors also found that approximately 53% of the variability in the placebo group was due to fluctuations within individual patients, as opposed to differences across the study population. This analysis supports the body of evidence suggesting that substantial variations in blood EOS count are common in patients with eosinophilic asthma. As a result, it is likely that repeated measurements of blood EOS may be necessary for the accurate diagnosis and effective management of eosinophilic asthma.

The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.

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