Assessment of the added value of basophil activation test in immediate drug allergy diagnosis.

Background. The diagnosis of immediate drug allergy (DA) relies on a combination of skin tests (ST), drug provocation tests (DPT), specific IgE levels (sIgE) and/or basophil activation tests (BAT). We aimed to compare BAT results with those of other allergy tests in patients with suspected immediate DA to a heterogeneous group of drugs, aiming to assess its diagnostic value. Methods. Patients who underwent BAT for suspected immediate DA at our hospital from January 2018 to December 2023 were included. Each case (suspected drug) was classified based on diagnostic tests performed - probable vs. improbable allergy (assessed by ST and/or sIgE only) or confirmed vs. excluded allergy (assessed by DPT). Inter-method agreement was assessed with Cohen's kappa index (κ). Results. Eighty-five patients were included: 51 female (60.0%), median age 53.0 years [interquartile range (IQR) = 33.0, Q1-Q3=31.0-64.0]. Median time elapsed since index reaction was 1.0 year [IQR=3.0, Q1-Q3 = 1.0-3.0]. We identified 112 suspected drugs: out of 16 cases with positive BAT (14.3%), 6 were probable (37.5%) and 1 confirmed allergy (6.3%). From 89 drugs with negative BAT (79.5%), 41 were improbable (46.1%) and 5 excluded allergy (5.6%). Seven agents had an inconclusive BAT (6.3%). A slight agreement (κ = 0.201) between BAT and other studies was observed when combining probable/improbable and confirmed/excluded results (n = 76). When limiting these findings to confirmed/excluded results (n=6), we found a perfect agreement (κ = 1).  Conclusions. We assessed BAT performance in a larger sample than those from previous studies. Slight agreement between methods increased to a perfect agreement when limiting to confirmed cases. Larger studies are needed to establish BAT's diagnostic value.