Association of Oxidative Stress Index With Disease Control During Omalizumab‐Based Treatment in Antihistamine‐Refractory Chronic Spontaneous Urticaria: A Prospective Observational Study

Chronic spontaneous urticaria (CSU) is monitored mainly with patient-reported outcomes, whereas objective biomarkers that reflect disease status remain limited. This prospective observational cohort study included 55 adults with antihistamine-refractory CSU who initiated omalizumab as part of routine clinical care and 30 healthy controls for baseline oxidative stress comparisons. Total antioxidant status (TAS), total oxidant status (TOS), and oxidative stress index (OSI) were measured at baseline and month 6, and at month 12 in patients requiring treatment escalation. Disease control, disease activity, and quality of life were assessed using validated instruments. Unadjusted baseline TOS and OSI were lower in patients than in controls, but these differences were attenuated and were no longer statistically significant after adjustment for age, sex, and BMI (log-TOS: β = -0.297, p = 0.115; log-OSI: β = -0.310, p = 0.102). Month-6 OSI was higher in uncontrolled than controlled patients [0.274 (0.162-0.382) vs. 0.135 (0.100-0.245) AU, p = 0.010] and remained associated with uncontrolled disease after adjustment for baseline OSI, BMI, CRP, total IgE, and angioedema presence (β = 0.572, p = 0.030). Within-person change in OSI correlated inversely with change in UCT (rho = -0.596, p < 0.001), whereas its association with change in CU-Q2oL did not reach statistical significance (rho = 0.264, p = 0.053). In the 15-patient escalation subgroup, OSI did not change significantly over time (Friedman p = 0.074). These exploratory findings indicate that on-treatment OSI was associated with concurrent disease control and that within-person OSI change paralleled change in UCT. Incremental value beyond validated patient-reported outcomes, predictive performance, and treatment-guiding value was not established.