Basophil and eosinophil dynamics as predictors of omalizumab resistance in chronic spontaneous urticaria

BACKGROUND: Chronic spontaneous urticaria is a mast cell-driven skin disorder in which basophils and eosinophils contribute to inflammation. Omalizumab is effective for many patients, yet a subset remains resistant. Hematologic markers such as eosinophil and basophil counts have been proposed as predictors, but their utility is unclear. AIM: This study aimed to investigate whether baseline levels and post-treatment changes in eosinophil and basophil counts can serve as predictors of omalizumab resistance in patients with chronic spontaneous urticaria. MATERIALS & METHODS: This retrospective study included forty adults with antihistamine-resistant chronic spontaneous urticaria treated with monthly omalizumab. Demographic, clinical, and laboratory data, including total immunoglobulin E and anti-thyroid peroxidase levels, were recorded. Absolute eosinophil and basophil counts were measured at baseline and after six months. Responders were defined as patients with a urticaria activity score ≤6 at month six. RESULTS: Thirty-four patients (85%) responded to omalizumab, while six (15%) were resistant. Baseline eosinophil and basophil counts tended to be lower in resistant patients, but differences were not significant. In non-responders, eosinophil and basophil counts increased significantly from baseline to month six (p = 0.002 and p = 0.007), whereas no significant changes occurred in responders. CONCLUSION: Increases in eosinophil and basophil counts during omalizumab therapy occurred mainly in non-responders, suggesting these changes may be associated with persistent disease activity rather than a direct treatment effect. However, given the limited number of non-responders in our cohort, these findings should be considered preliminary and require confirmation in larger prospective studies.