6.2.c. Value of in vitro tests
To date, there are no studies on the determination of specific IgE antibodies to PPI and, therefore, they are not available in the most widely used commercial platform for specific IgE determination to drugs, the ImmunoCAP system (Thermo-Fisher, Uppsala, Sweden). A promising tool for the diagnosis of immediate allergic reactions to PPI is the basophil activation test (BAT)19,21,38, which determine the basophil activation upon stimulation with the culprit drug or its metabolites by flow cytometry. \soutFor that Different strategies to identify basophils (anti-IgE, CCR3, CRTH2 and CD203c) and to measure their activation (CD63 and CD203c) have been proposed.62 Gamboa et al. were the first to report a positive BAT result to omeprazole in a patient who developed immediate urticaria and angioedema after the drug intake, result concordant with the positive skin test result.21 Later, a second case report of a patient with anaphylaxis after omeprazole administration confirmed the usefulness of BAT by detecting a positive result for the culprit PPI and negative results in healthy controls.38 Laguna et al. analyzed in detail the role of BAT, using CD63, for the diagnosis of 42 patients with immediate omeprazole allergy confirmed by ST or DPT and 22 age- and sex-matched healthy controls.19 They detected a BAT sensitivity of 73.8%, a specificity of 100%, a PPV of 100% and a NPV of 66.7%. Moreover, BAT was positive in 57.1% of patients with negative ST and by combining ST and BAT it was possible to reach a confident diagnosis of PPI HSRs in 85.7% of patients. There are no studies with other PPIs.