COMPARISON BETWEEN 2 AUTOMATED SYSTEMS TO DETERMINE SPECIFIC IGE - CAP AND ELITEST

Background and objective The ELItest(R) is a newly developed system to measure specific IgE based on allergen bound to paper rings and an al kaline phosphatase conjugated second antibody detection system. It was compared to the CAP(R) system, a method based on allergen conjugated to an encapsulated cellulose polymer and a beta-galactosidase conjugat ed fluorescence detection system. Methods Sera of 300 patients with po sitive history and positive skin-prick tests to common allergens (birc h, timothy-grass, cat dander, dermatophagoides pteronyssinus, wasp ven om) and 30 negative controls were tested in both systems. Serial dilut ions of high titre sera were measured; inter- and intraassay coefficie nts of variation (cv) were determined. Results The CAP system proved t o be more sensitive (92.3%) compared to ELItest (84%) but marginally l ess specific (94.7% for CAP versus 96.7% for ELItest). Intraassay cv w ere slightly lower in the ELItest (7.2% CAP versus 6.4% ELItest), wher eas the interassay cv was roughy twice as high for ELItest (20.1%) tha n for the CAP system (11.4%). Linearity over an 8-fold dilution was go od in both tests (r(2) 0.979 ELItest versus 0.996 CAP), although ELIte st levelled off at higher allergen concentrations. Similarly, correlat ion analysis between both systems revealed that ELItest consistently m easured lower values, especially at higher concentrations of specific IgE. The slope of the linear regression line of a log/log plot of meas ured IgE concentrations was significantly lower than 1 in birch, cat a nd wasp; the y-intersect was significantly lower than 0 in all analyse d allergens. Conclusion These results suggest that the ELItest system for the measurement of specific IgE is not quite as reproducible and s ensitive as the CAP system but slightly more specific, and that higher concentrations of specific IgE are measured lower in the ELItest. One potential reason might be that the amount of allergen bound to a pape r ring might be smaller than that bound to a cellulose polymer, but fu rther experiments are necessary to prove this hypothesis.