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Introduction: The possible influence of sensitization to aeroallergens on omalizumab response in chronic spontaneous urticaria (CSU) has been insufficiently investigated. This study's aim was to investigate atopy's influence on omalizumab response in CSU patients., Method: Retrospective study of CSU patients followed at a Portuguese Urticaria Center of Reference and Excellence (UCARE), treated with omalizumab for at least 6 months, between 2015 and 2022. At T0, all patients underwent quantification of specific immunoglobulin E (IgE) for total extract of most prevalent aeroallergens (ImmunoCAP Thermo Fisher Scientific®) and were divided in 2 groups, according to their response to omalizumab during the first 16 weeks of treatment: responders (R) (UAS7 <7) versus partial (PR) (UAS7 = 7-15) and nonresponders (UAS7 >15). R were further classified as fast (FR) (4-6 weeks) and slow responders (SR) (12-16 weeks). Total serum IgE, circulating eosinophil, and basophil counts were compared between groups at T0. p < 0.05 was considered statistically significant (SPSS® v25.0)., Results: Ninety-six patients (80% female) were studied, mean age 49 ± 14 years. Median CSU duration pre-omalizumab was 3 (0.6-20) years and mean omalizumab treatment duration was 3.7 ± 2.3 years. 38 (40%) had concomitant chronic inducible urticaria and 72 (75%) angioedema. Based on positive results of the specific IgE assay, 35 patients (36%) were considered atopic. Most patients (n = 30; 86%) were sensitized to house dust mites (HDM) (Dermatophagoides farinae = 28, Dermatophagoides pteronyssinus = 27, Blomia tropicalis = 19, Lepidoglyphus destructor = 17), followed by pollens (n = 12; 34%) (mixture of grasses = 10, Olea europaea = 7, Parietaria officinalis = 6), epithelia (n = 9; 26%) (dog = 8, cat = 7), and fungi (Alternaria alternata = 4; 11%). Eight patients (23%) were monosensitized to HDM and 4 (11%) to pollens. No significant association was found between aeroallergen sensitization and CSU duration, concomitant chronic inducible urticaria, or angioedema. Atopic patients featured significantly higher levels of baseline total serum IgE than nonatopic (469 vs. 94 U/mL, respectively; p = 0.0009). Mean baseline counts of eosinophils and basophils were not significantly different between atopic and non-atopic, respectively: eosinophils (128 vs. 121/mm3) and basophils (26 vs. 28/mm3). Regarding response to omalizumab, most patients (58; 60%) were responders: FR - 46 (79%); SR - 12 (21%). There was no significant association between aeroallergen sensitization and omalizumab response or speed of response., Conclusions: As far as we know, this is the first study exploring the influence of atopy sensitization pattern on omalizumab response in CSU. According to our results, presence of atopy/sensitization pattern does not influence omalizumab response in CSU patients., (© 2023 S. Karger AG, Basel.)