Background: Correct identification of the culprit venom is a prerequisite for specific venom immunotherapy.

Objective: To assess whether the basophil activation test (BAT) constitutes an additional diagnostic instrument in patients with equivocal or negative specific immunoglobulin (Ig) E or venom skin test (VST) results.

Methods: One hundred eighteen patients with a compelling history of IgE-mediated hymenoptera venom allergy were enrolled. Venomspecific IgE was quantifi d by ImmunoCAP and VST was performed in all patients. Basophil activation was analyzed by flow cytometry after labeling with anti-IgE and anti-CD63.

Results: In 64 out of 118 patients, diagnosis was considered as definite and the entomologic description was confi med by unequivocal and
concordant positive specifi c IgE and VST results. In 53 of those 64 patients, BAT confi rmed diagnosis, whereas the remaining 11 patients were nonresponsive in the BAT analysis. Forty-seven patients (40%) had a tentative diagnosis of venom allergy, as they had divergent specific IgE or VST results. In 31 of those patients, BAT was positive only for the suspected venom and helped to establish diagnosis of wasp and honeybee venom allergy in 28 and 3 patients, respectively. BAT was diagnostic in 7 patients with complete negative results for specific IgE and VST, despite clear entomologic identification.

Conclusions: In about half the patients with diagnosis of venom allergy, unequivocal specific IgE and VST results are obtained and additional tests are not needed. In the remainder, diagnosis is less straightforward due to discrepant or negative specific IgE or VST results. In these patients, BAT constitutes a helpful additional instrument to identify the culprit venom and start venom immunotherapy accordingly.

Key words: Anaphylaxis. CD63. Basophil activation test. Flow cytometry. Immunoglobulin E. Immunotherapy. Skin test.