Correlation of the diagnostic skin test with the immunoperoxidase assay in ragweed hypersensitivity

The results of the diagnostic skin test are correlated with those obtained with an immunoperoxidase (IP) assay in 77 patients with positive histories for ragweed hay fever. The IP assay, a version of the ELISA technique, employs polystyrene microtiter plates as the solid-phase, horseradish peroxidase as the enzymatic label and O-phenylene diamine as the enzyme substrate. Concordance between the results of these two diagnostic techniques was observed in 66 patients (86%). Among the 11 patients with discordant results the modified RAST test was in agreement with the IP assay in 7 and with the diagnostic skin test in 4 patients. In these latter 4 patients ragweed-specific IgE antibodies were detected by the IP or the modified RAST assays in low titers. The coefficients of variation for the IP assay ranged from 8% to 14.3%. The pros and cons of the use of in vitro tests (the IP and the RAST test) and the diagnostic skin test in clinical practice of allergy are discussed.