Cellular in vitro assays in the diagnosis of Hymenoptera venom allergy

BACKGROUND: The current diagnostic procedures of anaphylactic reactions to hymenoptera stings include intradermal tests, venom-specific IgE (sIgE) and possibly sting challenge tests. Sometimes, the culprit insect remains unidentified. The usefulness of the cellular assays CAST-ELISA and Flow-CAST in the management of hymenoptera venom allergy was investigated. METHODS: 134 patients with systemic reactions after a yellow jacket wasp and/or honey bee sting and 44 healthy controls underwent skin tests, as well as determination of sIgE (CAP-FEIA), leukocyte sulfidoleukotriene release (CAST-ELISA) and basophil CD63 expression (Flow-CAST) upon insect venom stimulation. The clinical diagnosis based on the history alone served as reference. Sensitivity, specificity, and positive and negative predictive value of all methods were compared. Concordance and correlations among methods were calculated. RESULTS: Sensitivity and specificity of all in vitro tests were consistently high. The combination of all tests (skin tests, sIgE, combined cellular assays) yielded a positive predictive value of 100% for both venoms, if all 3 were positive, and a negative predictive value of 100%, if at least 1 test was positive. Relative specificities were considerably higher for the cellular assays (honey bee: CAST 91.1%, Flow-CAST 85.7%; yellow jacket wasp: CAST 98.4%, Flow-CAST 92.1%) and allow the detection of the culprit insect in patients with reactivity to both insects. The concordance between methods was good. There is no correlation between severity of clinical reaction and cellular assays. CONCLUSION: CAST-ELISA and Flow-CAST are valuable additional diagnostic tools for establishing the true culprit insect in patients with unclear clinical history or sensitization to both insects.