Predictors of response to omalizumab in chronic spontaneous urticaria: a retrospective cohort study.

Introduction: Although omalizumab is a highly effective treatment against chronic spontaneous urticaria (CSU), the treatment duration for response varies among patients. Thus, determining easy-to-access predictive biomarkers of omalizumab response is essential.

Objective: This study aimed to investigate the value of baseline hematological and inflammatory parameters and patient-specific features as predictive markers of response to standard-dose omalizumab.

Methods: This single-center retrospective cohort study was conducted on 242 patients with CSU treated with omalizumab 300 mg every 4 weeks for at least 6 months between 2014 and 2025. The demographics, clinical features, treatment responses, and baseline laboratory tests were assessed. Response to omalizumab was evaluated based on the weekly Urticaria Activity Score (UAS7). Patients were categorized as early responder (ER, within 3 months), late responder (LR, after 3 months), and nonresponder (NR).

Results: Of patients, 180 (74.4%) were classified as ER, 28 (11.6%) as LR, and 34 (14%) as NR. ERs had higher white blood cell (WBC) and lymphocyte counts (p = 0.047 and p = 0.005, respectively) and lower mean platelet volume (MPV)/lymphocyte ratio (MPVLR) (p = 0.008). LRs had higher mean corpuscular hemoglobin concentration (MCHC) and platelet/lymphocyte ratio (PLR) (p = 0.023 and p = 0.014, respectively) and lower MPV levels (p = 0.043). The platelet distribution width (PDW) was higher in the NRs (p = 0.011). Red cell distribution width-coefficient of variation (RDW-CV) [odds ratio (OR): 0.793, 95% confidence interval (CI): 0.641-0.980, p = 0.032], WBC count (OR: 1.418, 95% CI: 1.093-1.840, p = 0.009), and PDW (OR: 0.813, 95% CI: 0.693-0.954, p = 0.011) were found to be the independent predictors of responders. The lymphocyte count (OR: 1.713, 95% CI: 1.122-2.613, p = 0.013) and MPVLR (OR: 0.427, 95% CI: 0.218-0.837, p = 0.013) were independent predictors of ER, whereas MCHC (OR: 2.368, 95% CI: 1.522-3.686, p < 0.001) and PLR (OR: 1.010, 95% CI: 1.003-1.017, p = 0.003) were independent predictors of LR. The receiver operating characteristic curve analysis results showed that the predictive strengths of RDW-CV, WBC count, PDW, lymphocyte count, MPVLR, MCHC, and PLR were low (the area under the curve values 0.634, 0.620, 0.672, 0.656, 0.621, 0.649, and 0.624, respectively; all p < 0.05), suggesting the limited use of these parameters in clinical practice.

Study limitations: The limitations of this study included its single-center, retrospective design, lack of external validation, and reliance solely on UAS7 for assessing disease activity.

Conclusions: WBC and lymphocyte counts, RDW-CV, PDW, MPVLR, MCHC, and PLR can be considered when appraising the omalizumab response. However, given their limited predictive strength, these parameters alone may not accurately predict the efficacy of omalizumab.