Background: New in vitro diagnostic methods for IgE-mediated drug allergic reactions, such as basophil activation test and antigen specific sulfidoleukotriene test, have proven their usefulness in patients with positive skin tests.

Objective: To assess the usefulness of basophil activation test and antigen specific sulfidoleukotriene test in the diagnosis of patients with IgE-mediated allergy to Betalactam antibiotics and negative skin tests.

Methods: The 23 patients included in the study underwent basophil activation test, antigen specific sulfidoleukotriene test and specific IgE. The patients were classified into three groups. Group A: patients with positive specific IgE. Group B: patients with a unique immediate reaction to Betalactams, negative specific IgE and positive oral provocation tests. And Group C: patients with at least two immediate reactions induced by Betalactams and negative specific IgE.

Results: The sensitivity/specificity of the different tests are: basophil activation test 39.1%/93.3%, antigen specific sulfidoleukotriene test 22.7%/83.3%, specific IgE 21.7%/86.7%. The joint use of the three tests allows diagnosis of 60.9% of the patients.

Conclusion: In vitro diagnostic tests, especially basophil activation test, are very important tools in the diagnosis of patients with IgE-mediated allergy to Betalactams and negative skin tests, avoiding performance of potentially dangerous oral provocation tests in a high percentage of cases.

Key words: Basophil activation test, Betalactams, Drug allergy, in vitro test, leukotriene, specific IgE, skin test.