Performance characteristics of a new automated enzyme immunoassay for the measurement of allergen-specific IgE. Summary of the probability outcomes comparing results of allergen skin testing to results obtained with the HYTEC system and CAP system.

Abstract

Measurement of allergen-specific IgE may assist in the diagnosis of allergy in selected patients. The development of new assays for determination of allergen-specific IgE should be optimized with respect to analytical sensitivity, precision, automation, and reporting of test results in mass units. The objectives of this study were to evaluate the analytical performance of the new automated HYTEC method for the measurement of allergen-specific IgE and to compare the performance of this new assay to that of the Pharmacia CAP system. To demonstrate parallelism, allergen-specific IgE dilution curves were generated by diluting four patient sera containing cat (19.8 kU/L), D. pteronyssinus (5.4 kU/L), birch pollen (2.6 kU/L), and timothy grass (1.0 kU/L) with equine serum. The precision study utilized sera from three different atopic donors with low levels (0.62 +/- 0.05 kU/L), moderate levels (1.45 +/- 0.18 kU/L), and high levels (13.59 +/- 0.89 kU/L) of allergen-specific IgE to three common inhalant allergens: D. pteronyssinus, timothy grass, and birch. Sera for outcome probability determinations were obtained from 54 patients who were evaluated for the presence of inhalant allergy by skin prick test and physical examination. Only sera from patients with at least one positive skin prick test that clinically correlate with the physician's evaluation of case history and physical examination were selected for study material. In this study, sensitivity and specificity are conditional probabilities describing performances of the CAP system and the HYTEC system to skin prick testing. The lowest threshold, 0.35 kU/L, recommended for detection of allergen-specific IgE was used for both systems. The HYTEC system accurately detected a reduction in allergen-specific IgE antibody with different serum concentrations of allergen-specific IgE ranging from 0.10 kU/L to 20 kU/L. The median interdilutional coefficient of variation of 12.5% was obtained with assay samples containing 19.8 to 0.1 kU/L allergen-specific IgE antibody. During a 20-day trial period, three standard allergen-specific IgE controls, 0.62, 1.45 and 13.39 kU/L, respectively, demonstrated a mean coefficient of variation less than 18%. In 20% of the patients, duplicate assay determinations of allergen-specific IgE measurements resulted in a one-class discrepancy in the lowest assay range, 0.35 to 0.70 kU/L, only. The correlation coefficient between the HYTEC and CAP allergen-specific IgE assays was 0.77, rank correlation coefficients, being allergen-dependent and ranging from 0.62 to 0.91. Allergen-specific IgE assay sensitivity of the HYTEC system ranged from 0.78 to 1.00, whereas the assay sensitivity for the CAP system ranged from 0.50 to 1.00. Assay specificity ranged from 0.66 to 0.93 for the HYTEC system and from 0.70 to 0.87 for the CAP system. Eighty-nine percent of HYTEC-positive patients had a positive skin prick test (3% standard error) and 87% of CAP-positive patients had a positive skin prick test (4% standard error). Ninety-two percent of HYTEC-negative patients had a negative skin prick test (4% standard error), whereas 76% of CAP-negative patients had a negative skin prick test (5% standard error). The HYTEC system fulfills the current analytical requirements necessary to measure allergen-specific IgE antibody quantitatively and qualitatively, and compares favorably in performance with the CAP system.