Serum tryptase level is a better predictor of systemic side effects than prostaglandin D2 metabolites during venom immunotherapy in children.

OBJECTIVES We performed a prospective study to analyze mast cell mediators as predictors of systemic adverse reactions during rush venom-specific immunotherapy (VIT) in children. PATIENTS AND METHODS Nineteen children aged 5-17 years received VIT with Venomenhal (HALAllergy). We analyzed serum tryptase (CAP, Phadia), plasma prostaglandin (PG) D2 metabolites (9alpha, 11beta-PGF2), and urine PGD2 metabolites (9alpha, 11beta-PGF2, tetranor-PGD-M) using gas chromatography mass spectrometry before and after the rush protocol. RESULTS Three boys with high baseline serum tryptase values (>7.76 g/L) (P < .001) and low 9alpha, 11beta-PGF2 concentrations developed grade III systemic adverse reactions during VIT. Baseline serum tryptase was lowest in children who had a Mueller grade II reaction (1.93 [0.36]) before VIT and highest in children with a Mueller grade III reaction (6.31 [4.80]) (P = .029). Repeated measures analysis of variance confirmed that, in children who developed systemic adverse reactions during VIT, serum tryptase was higher both before and after desensitization and increased significantly following the procedure. Analysis of PGD2 metabolites in the prediction of systemic adverse reactions during VIT was inadequate (sensitivity 67% and specificity 0.53%), whilst prediction based on serum tryptase was accurate. CONCLUSIONS In children with severe systemic adverse reactions to Hymenoptera sting, the evaluation of baseline tryptase levels should be a standard procedure. Children with Apis mellifera venom allergy and baseline tryptase levels higher than 7.75 g/L are at risk of anaphylaxis during buildup. Lower baseline values of plasma and urinary PGD2 metabolite concentration in patients with systemic adverse reaction during VIT suggest that prostaglandin catabolism is altered.