Serum Eosinophil Level Correlates With Atopic Dermatitis Severity: A Multicenter Cross‐Sectional Study in Chinese Patients With a Nested Cohort Analysis of Dupilumab Treatment Response

Background Personalized treatment strategies for atopic dermatitis (AD) are limited. Although serum total IgE (tIgE) and blood eosinophil levels are proposed biomarkers for AD severity, their clinical utility requires validation. Objectives We aimed to identify biomarkers reflecting AD severity and their association with dupilumab efficacy. Methods In this multicenter cross‐sectional study, 387 AD patients of all ages were stratified by severity (Investigator's Global Assessment, Numerical Rating Scale [NRS], Body Surface Area [BSA]). Multivariate logistic regression analyzed associations between demographic/clinical factors (age, gender, BMI, tIgE, eosinophils) and disease severity or dupilumab response (EASI75, NRS improvement). Results Age and eosinophil levels correlated significantly with BSA severity ( p = 0.045; p = 0.014), while gender, BMI, and tIgE showed no association. Elevated eosinophils predicted poorer dupilumab efficacy at week 2 (EASI75: OR = 0.269, p = 0.033). Early pruritus relief (NRS ≥ 4‐point reduction) at week 2 was associated with older age (OR = 1.024, p = 0.026), higher tIgE (OR = 1.001, p = 0.005), and female gender (OR = 0.357, p = 0.004). These associations persisted at weeks 4–6 but diminished by weeks 9–12. Limitations This study is limited by poor generalizability (particularly in children and older adults, precluding age‑stratified analysis), treatment selection bias related to cost and accessibility, and incomplete dupilumab follow‑up efficacy data. Conclusions Blood eosinophil levels, but not tIgE, may serve as a biomarker for AD severity and early dupilumab response. Demographics influence short‐term outcomes, highlighting the need for individualized monitoring.