Comparison between specific IgE measured by RAST, two chemiluminescent assays and skin prick test

Two hundred adult patients referred to a regional outpatient allergy clinic were skin prick tested and their specific IgE against ten inhalant allergens was measured by three different assays: the classical radioallergosorbent assay, Phadebas RAST (P-RAST), (Pharmacia AB, Uppsala, Sweden), the multi-allergosorbent chemiluminescent assay CLA (MAST), (Dome/Hollister-Stier, Miles Ltd., UK), and the immunocheminometric assay, MAGIC LITE SQ Specific IgE (ML), (ALK Laboratorierne, Hørsholm, Denmark). Skin prick test (SPT) was performed with extracts from the same companies. Marked differences between the assays were seen especially in the low range. Specific IgE was detected in 17% of the samples by P-RAST, in 66% by CLA, and in 17% by ML. Frequency distribution of P-RAST and ML measurements showed a peak at zero and a gradual decline towards larger values, whereas distribution for CLA was U-shaped with a peak at zero and another peak close to maximum reactions. Kendall's rank correlation coefficient being 0.80 for P-RAST vs. CLA. Correlation coefficient between measurements of specific IgE and SPT was high for CLA (0.65). Even in the low-level subgroup where IgE was detected by CLA only, a high correlation (0.60) between CLA and SPT was observed. In conclusion marked differences were observed between the three assays for specific IgE measurement. The CLA system seems to be more sensitive than the conventional P-RAST and ML, but further studies should reveal whether this extra sensitivity is clinically useful.