Development and validation of a third generation allergen-specific IgE assay on the continuous random access IMMULITE...

In vitro determination of allergen-specific IgE (sIgE) represents an important aid in the diagnosis and treatment of allergy. Improvements in laboratory methodology--the development of second, and now third generation assays for sIgE--have brought about major advances in speed, convenience, performance, and in the standards for judging performance. In this study, following the NCCLS I/LA20-A guidelines, we evaluated the analytical performance of a quantitative chemiluminescent enzyme immunoassay for sIgE using the continuous random access IMMULITE 2000 system. Defining features of this "third generation" sIgE assay include a true zero calibrator with a detection limit and functional sensitivity of 0.1 and 0.2 kU/L, respectively. The use of liquid allergens allows for complete automation, fast binding kinetics between IgE and the natural allergenic protein conformations, and a time-to-first-result of 65 min. Stable reagents and the low nonspecific signal associated with the liquid allergens and centrifugal wash technique permit extension of the measuring range to 0.1-100 kU/L, based on lot-specific, factory-calibrated master curves standardized to the WHO 75/502 reference standard. The assay demonstrated good precision and linearity over its measuring range. Relative to a first generation RIA (mRAST, from Hycor), clinical sensitivity, specificity, and concordance were 88%, 92%, and 90%, respectively (n = 812). Quantitative comparisons to a second generation assay yielded a linear regression relationship of IMMULITE 2000 = 0.99 (Pharmacia FEIA) + 1.99 kU/L, r = 0.859 (n = 169).