DETERMINATION OF IGE ANTIBODIES TO THE BENZYLPENICILLOYL DETERMINANT - A COMPARISON OF THE SENSITIVITY AND SPECIFICITY OF 3 RADIO ALLERGO SORBENT TEST METHODS

The quantitation of in vitro IgE antibodies to the benzylpenicilloyl d eterminant (BPO) is a useful tool for evaluating suspected penicillin allergic subjects. Although many different methods have been employed, few studies have compared their diagnostic specificity and sensitivit y. In this study, the sensitivity and specificity of three different r adio allergo sorbent test (RAST) methods for quantitating specific IgE antibodies to the BPO determinant were compared. Thirty positive cont rol sera (serum samples from penicillin allergic subjects with a posit ive clinical history and a positive penicillin skin test) and 30 negat ive control sera (sera from subjects with no history of penicillin all ergy and negative skin tests) were tested for BPO-specific IgE antibod ies by RAST using three different conjugates coupled to the solid phas e: benzylpenicillin conjugated to polylysine (BPO-PLL), benzylpenicill in conjugated to human serum albumin (BPO-HSA), and benzylpenicillin c onjugated to an aminospacer (BPO-SP). Receiver operator control curves (ROC analysis) were carried out by determining different cut-off poin ts between positive and negative values. Contingence tables were const ructed and sensitivity, specificity, negative predictive values (PV-), and positive predictive values (PV+) were calculated. Pearson correla tion coefficients (r) and intraclass correlation coefficients (ICC) we re determined and the differences between methods were compared by chi (2) analysis. Analysis of the areas defined by the ROC curves showed s tatistical differences among the three methods. When cut-off points fo r optimal sensitivity and specificity were chosen, the BPO-HSA assay w as less sensitive and less specific and had a lower PV-and PV+ than th e BPO-PLL and BPO-SP assays. Assessment of r and ICC indicated that th e correlation was very high, but the concordance between the PLL and S P methods was higher than between the PLL and HSA or SP and HSA method s. We conclude that for quantitating IgE antibodies by RAST to the BPO determinant, BPO-SP or BPO-PLL conjugates offer advantages in sensiti vity and specificity compared with BPO-HSA. These results support and extend previous in vitro studies by our group and highlight the import ance of the carrier for RAST assays. (C) 1997 Wiley-Liss, Inc.