Validation of a flow cytometric assay detecting in vitro basophil activation for the diagnosis of muscle relaxant allergy

Background: Anaphylactic reactions during anesthesia are mainly the result of muscle-relaxant (MR) drugs. Skin tests, serologic detection of specific IgE, and in vitro leukocyte histamine release are used to investigate MR al lergy. Objective: We describe a new assay that is based on the detection, by flow cytometry of the altered expression of plasma membrane molecules of MR-acti vated basophils. Methods: For this assay, which we have named the BASIC assay, basophils are incubated in vitro with MR, after which they are fixed and then triple lab eled with fluorescein-conjugated anti-CD63, tandem dye R-phycoerythrin-cyan in 5.1 conjugated anti-CD45, and R-phycoerythrin conjugated anti-IgE. The r esulting Basophils' Altered Surface Immunofluorescence is detected by flow Cytometry (BASIC). Results: Forty-one patients who had an allergic reaction during general ane sthesia and 23 control subjects without such a history were studied. All in cluded subjects' basophils were tested in the BASIC assay with at least 4 M R: suxamethonium, gallamine, vecuronium, and pancuronium. After reaction of the basophils of the MR-allergic patients with MRs, increased surface expr ession of CD63 and CD45 and decreased expression of IgE were detected. Incr eased expression of CD63 was observed most frequently and it was stronger t han the alteration of the 2 other markers. Cross-reactivity between MRs com monly occurred. MRs diluted 10(-1) activate the basophils of the control su bjects, suggesting that at relatively high concentrations MRs are also nons pecific basophil activators. Conclusion: In the diagnosis of MR allergy, the BASIC assay has a good spec ificity but a low sensitivity, and it correlates strongly with skin test re sults. It is currently appraised for the diagnosis of anaphylactic reaction induced by other classes of drugs.