Baseline Blood Eosinophil Count Does Not Predict Short-Term Changes in Oscillometric Parameters in Steroid-Naïve Asthma

Background
Peripheral blood eosinophil (PBE) count is widely used as a biomarker to guide treatment decisions in asthma. However, whether eosinophil levels predict early changes in airway mechanics assessed by oscillometry remains unclear, particularly in steroid-naïve patients.
Objective
To determine whether baseline PBE levels are associated with early changes in oscillometric indices of airway function in steroid-naïve asthma.
Methods
We retrospectively analyzed adult patients with steroid-naïve asthma who underwent oscillometry at baseline and after 12 weeks of inhaled corticosteroid–based therapy. Patients were stratified according to baseline PBE count (≥300 vs <300 cells/μL). Percentage changes in R5, R20, R5–R20, X5, resonant frequency (Fres), and area of low-frequency reactance (ALX) were compared using the Mann–Whitney U test. Effect sizes were estimated using the Hodges–Lehmann method with exact confidence intervals.
Results
A total of 57 patients were included (n = 33 with eosinophils ≥300 cells/μL; n = 24 with eosinophils <300 cells/μL). No significant differences were observed between groups in percentage changes of oscillometric parameters. Hodges–Lehmann estimates of group differences were small, and all confidence intervals crossed zero, indicating no clinically meaningful association between baseline eosinophil levels and early oscillometric improvement.
Conclusions
In steroid-naïve asthma, baseline PBE count does not appear to predict early changes in oscillometric indices. These findings suggest that baseline PBE counts may be informative for spirometric responses to inhaled corticosteroid–based therapy, whereas their utility for anticipating early changes in oscillometric indices is limited. Spirometry and oscillometry may therefore provide complementary, rather than interchangeable, information when assessing early treatment responses in asthma.