Relevance of the basophil activation test in a cohort of 240 patients with chronic spontaneous urticaria.

Background: The basophil activation test (BAT) is considered to be the best biomarker to predict autoimmune chronic spontaneous urticaria (aiCSU). To date, few studies have investigated the utility of BAT in real-world clinical practice, the role of aiCSU biomarkers in relation to omalizumab therapy and the degree of association between different aiCSU tests.

Objectives: To analyse the clinical and laboratory features of a prospective cohort with chronic spontaneous urticaria (CSU) according to their BAT status, as well as to study omalizumab efficacy according to aiCSU biomarkers.

Methods: A prospective study was conducted from 2010 to 2024 in patients with CSU. BAT alongside other laboratory tests were performed, and clinical and therapeutic features were prospectively collected. Data obtained were compared according to BAT status (positive vs. negative). Furthermore, omalizumab drug survival was typified according to aiCSU biomarkers.

Results: In total, 240 patients were included in the study. Patients who were BAT positive presented more frequently with low IgE levels, higher occurrence of IgG antithyroid peroxidase (anti-TPO) positivity, autologous serum skin test (ASST) positivity, basopenia and eosinopenia. Multivariate logistic regression revealed that ASST [odds ratio (OR) 7.69, 95% confidence interval (CI) 2.81-21.0] and anti-TPO (OR 2.63, 95% CI 1.05-6.61) were associated with BAT positivity. All aiCSU biomarkers (BAT, ASST, combined ASST/BAT positivity and low IgE/anti-TPO+) were associated with significantly shorter omalizumab survival because of treatment failure. In the cohort, both low IgE/anti-TPO+ and ASST were associated with BAT positivity.

Conclusions: The use of BAT in clinical practice delineates a subgroup of patients with specific clinical, laboratory and therapeutic features, including increased omalizumab failure.