Sensitization to Hymenoptera venoms is common, but systemic sting reactions are rare.

Background: Sensitization to Hymenoptera venom without systemic sting reactions (SSRs) is commonly observed in the general population. Clinical relevance for a future sting has not yet been investigated.

Objective: We aimed to evaluate the effect of these debatable sensitizations with deliberate sting challenges and to monitor serologic changes for up to 2 years.

Methods: One hundred thirty-one challenges with bees and wasps were performed in 94 subjects with a hitherto irrelevant sensitization. The clinical outcome was recorded, and results of specific IgE (sIgE) determinations, skin tests, and basophil activation tests were correlated to the sting reaction. sIgE levels were monitored in reactors and nonreactors after 3 hours, 1 week, 4 weeks, and 1 year.

Results: Only 5 (5.3%) patients had SSRs, but 41 (43.6%) had large local reactions (LLRs) after the sting. Compared with the general population, there was a 9.5-fold higher risk for LLRs but not for SSRs. Three hours after the sting, sIgE levels slightly decreased, but none of the 94 subjects' results turned negative. After 1 week, sIgE levels already increased, increasing up to 3.5-fold (range, 0.2- to 34.0-fold) baseline levels after 4 weeks. To assess the clinical relevance of this increase, we randomly selected 18 patients for a re-sting. Again, 50% had an LLR, but none had an SSR.

Conclusion: Although sensitization to Hymenoptera venoms was common, the risk of SSRs in sensitized subjects was low in our study. The sIgE level increase after the sting was not an indicator for conversion into symptomatic sensitization. Currently available tests were not able to distinguish between asymptomatic sensitization, LLRs, and SSRs.