Predictors of response to omalizumab and relapse in chronic spontaneous urticaria: a study of 470 patients

Background: Chronic spontaneous urticaria (CSU) is defined as spontaneous occurrence of wheals and/or angioedema for ≥6 weeks. Omalizumab is a monoclonal anti-IgE antibody effective in refractory CSU, but its mechanism of action and markers predictive of response remain not completely defined. Objectives: To correlate baseline levels of two proposed biomarkers, total IgE (bIgE) and d-dimer (bd-dimer), and clinical parameters to omalizumab response and to relapses after drug withdrawal. Methods: In this retrospective Italian multicentre study, clinical data were collected in 470 CSU patients, and bIgE and bd-dimer were measured in 340 and 342 patients, respectively. Disease activity was determined by Urticaria Activity Score 7 (UAS7) at week 1 and 12 after omalizumab starting. Relapses were evaluated during a 2- and 3-month interval after a first and a second course of treatment, respectively. Results: bIgE correlated to a good response to omalizumab since levels were significantly higher in responders than non-responders (P = 0.0002). Conversely, bd-dimer did not correlate to response. There was no correlation between both bIgE and d-dimer and either first or second relapse. Disease duration was significantly longer in patients who experienced either first or second relapse (P < 0.0001 and P = 0.0105, respectively), while baseline UAS7 correlated only to first relapse (P = 0.0023). Conclusions: Our study confirms bIgE as a reliable biomarker predicting response to omalizumab in CSU, while it does not support the usefulness of bd-dimer unlike previous findings. CSU duration before omalizumab and baseline UAS7 may be clinical markers of relapse risk.