Correlation of a micro-ELISA assay with the skin test and the RAST assay in inhalant allergy

Several modifications of a previously described micro-ELISA assay (IP Assay) for the diagnosis of IgE mediated disorders were developed to increase the assay sensitivity and specificity. The absorbance values in milliunits obtained in this assay were normalized with a computer algorithm. The results of this assay correlate well with those obtained with the RAST assay (normalized milliunits of absorbance versus bound radioactivity: r = 0.74 to 0.87). However, the IP assay detected allergen specific IgE antibodies in many sera for which the RAST assay gave negative results (from 13.3% to 28% for a variety of allergens). The converse was seen in fewer than one percent of tests. Further, in a series of 300 tests for a panel of ten allergens, the IP assay showed a higher degree of correlation with the intradermal skin test (82%) than the RAST assay (77.3%). The specificity of the IP and RAST assays were comparable. Data showing the stability of the polystyrene surface immunosorbent and the independence of the IP assay from high levels of total IgE antibodies are presented. The reasons for higher sensitivity of the IP assay than the RAST assay (and hence superior correlation with the skin test) are discussed.