Comparison of three in vitro assays for serum IgE with skin testing in asthmatic children

The diagnostic performance of three commercial assay kits [Phadezym RAST (PhRAST), Pharmacia CAP system (CAP), and multiple chemiluminescent assay (CLA-MAST)] for measuring serum-specific IgE was evaluated and compared using intradermal skin testing or skin prick testing as reference standards. Serum samples were obtained from allergic patients who were tested with either intradermal skin tests or skin prick tests (96 and 49 subjects, respectively). Six different allergen extracts were tested: Dermatophagoides pteronyssinus, Candida albicans, Aspergillus, short ragweed, Bermuda grass, and cockroach mix. Results showed that when using intradermal skin testing as a reference standard, the CLA-MAST had the lowest sensitivity (75%), specificity (80%), and efficiency (85%) but the Pharmacia CAP system achieved the highest sensitivity, specificity, and efficiency (86%, 94%, and 91%, respectively). When compared with these two relatively new assays, the Phadezym RAST had medium sensitivity (80%), specificity (92%), and efficiency (88%). In contrast, when using skin prick testing as a reference standard, the highest specificity was achieved by Phadezym RAST (95%), followed by Pharmacia CAP system (90%), and MAST (81%). As for the sensitivity of each test, the Phadezym RAST was the lowest (60%) and Pharmacia CAP system reached the highest sensitivity (79%); and for the efficiency test, the score was 87% for CAP, 83% for Phadezym RAST, and 75% for MAST. These results suggest, therefore, that the CAP system is the preferred test and provides a useful guide for prescription of environmental control and immunotherapy in unselected patients.