D3.414 - Clinical and Laboratory Predictors of Basophil Activation Test Positivity in Chronic Spontaneous Urticaria: A Real-World Exploratory Study

Chronic spontaneous urticaria (CSU) is a heterogeneous condition with distinct immunological endotypes. A subset of patients presents features consistent with autoimmune CSU (type IIb), characterized by functional autoantibodies against FcεRI or IgE. The basophil activation test (BAT) has emerged as a potential functional biomarker of this endotype; however, its availability is limited and its clinical predictors remain insufficiently defined. 

Objective:

To identify clinical and laboratory parameters associated with BAT positivity in patients with CSU in a real-world tertiary center cohort.

We conducted a retrospective observational study including adult patients with CSU who underwent BAT testing. Demographic data, clinical features (angioedema, inducible component, atopy), baseline disease activity (Urticaria Control Test - UCT, Dermatology Life Quality Index - DLQI), and laboratory parameters (total IgE, peripheral eosinophil and basophil counts, D-dimers, and autoimmune markers including anti-thyroid antibodies when available) were collected. Patients were stratified according to BAT result (positive vs negative). Continuous variables were compared using non-parametric tests and categorical variables using Fisher’s exact test.

Twenty patients were included (all female; median age of 47 years, std 14.3). Two patients (10%) were BAT-positive. BAT-positive patients showed a trend toward lower total IgE levels and reduced peripheral basophil counts compared with BAT-negative individuals. Autoimmune markers were more frequently observed among BAT-positive patients. Baseline disease activity scores (UCT and DLQI) did not demonstrate a clear separation between groups, although BAT-positive patients tended to present with moderate-to-severe impairment. No consistent differences were observed regarding atopic status, or presence of inducible urticaria.

Our findings highlight a distinct laboratory profile among BAT-positive patients, characterized by low total IgE and basopenia, consistent with previously described features of autoimmune CSU. While limited by the small sample size, this real-world observation underscores the biological heterogeneity of CSU and the need for practical tools to better characterize its underlying endotypes.