Background Current guidelines do not adequately address the question of how best to manage patients with a convincing history of insect allergy, but negative venom-specific IgE and skin test results.
Methods Forty-seven patients out of a total of 1219 (4%), with a positive history of sting allergy, were recruited over a period of 4.5 years. All recruited patients had a convincing history of a severe or a life-threatening anaphylactic reaction of Mueller grade II–IV (median grade III) after Hymenoptera sting, but negative venom-specific IgE and skin prick test results. Diagnostic work-up was prospectively followed by the CD63 basophil activation test and by intradermal skin testing. A control group of 25 subjects was also assessed.
Results Thirty-five out of 47 (75%) patients demonstrated a positive basophil CD63 response after stimulation with bee and/or wasp venom. Intradermal venom skin tests were performed for 37 patients, 17 (46%) of whom showed positive results. Out of 20 patients who demonstrated negative intradermal test results, 12 patients showed a positive CD63 response (60%). In contrast, out of 9 patients who showed a negative CD63 response, only one was detected by intradermal testing (11%). In the control group, only two out of 25 (4%) subjects displayed a positive basophil response and/or intradermal test.
Conclusion Here we show that, in complex cases with inconclusive diagnostic results, the CD63 activation test could be particularly useful and more sensitive than intradermal skin testing.