- D1.523 - Clinical characterization of patients with Hymenoptera venom allergy undergoing venom immunotherapy stratified by basal serum tryptase

Hymenoptera venom allergy (HVA) is a major cause of anaphylaxis. Systemic mastocytosis (SM) and elevated basal serum tryptase (BST) are recognized risk factors for severe reactions. The relationship between BST, specific Immunoglobulin E (IgE) levels and skin test results in HVA is yet to be fully characterized.

We aimed to characterize clinical aspects, reaction severity and diagnostic findings of patients with HVA according to BST.

Retrospective analysis of patients followed in our Allergy Unit for HVA. Patients were stratified into three groups based on BST: SM, normal BST and elevated BST without SM. Clinical data, total IgE, venom-specific IgE, skin prick tests (SPT), intradermal tests (IDT) and reaction severity (according to Mueller scale) were analyzed. Cut-off values were 0.35kU/L for venom-specific IgE and 11.4ug/L for BST.

Our study included 57 patients, mean age 53.9±14.1 years, 70.2% male, 14% beekeepers. Venom allergies included honeybee (35.1%), wasp (31.6%), paper wasp (8.8%) and Asian hornet (21.1%). All patients were receiving venom immunotherapy, with 5.9% requiring adjunctive omalizumab.

The SM group had significantly lower honeybee-specific IgE compared to the normal BST group (p=0.014). No significant differences were observed in other venom-specific IgE or total IgE across groups. BST did not differ significantly between SM and elevated BST groups (p=0.465). Severe reactions (Mueller grade III-IV) predominated across all groups, with 100% observed in the SM patients versus 87.3% in the normal BST group and 80% in the elevated BST group, with no statistically significant differences. IDT showed higher positivity rates than SPT across groups, without significant differences.

Age did not differ significantly among groups (p=0.49) and a predominance of male patients was observed across the groups.

Patients with SM had lower honeybee-specific IgE levels despite severe reactions, reinforcing that IgE levels do not predict clinical severity; non-significant findings for other venoms may reflect limited statistical power.

Our findings support the measurement of BST in all patients with HVA and highlight the added diagnostic value of IDT to SPT. In patients with low or negative venom-specific IgE, basophil activation testing may be a useful complementary diagnostic tool. Despite the limited sample size, these results emphasize the importance of combining multiple diagnostic modalities for accurate risk stratification in HVA management.