Comparison of Modified PhadezymRAST,* ImmunoCAP,* and serial dilution titration skin testing by receiver operating curve analysis

Abstract

Improved technology in in vitro tests for allergen-specific immunoglobulin E has led to increased efficiency and faster turnaround times. ImmunoCAP (Pharmacia Diagnostics, Clayton, N.C.) is an in vitro–specific immunoglobulin E test that uses a three-dimensional cellulose solid allergen phase, which allows quick results in 6 hours. In comparison, modified PhadezymRAST (Pharmacia Diagnostics) uses a two-dimensional solid phase, and results take 3 days to obtain. This study compares the sensitivity and specificity of CAP with that of modified RAST in the detection of specific immunoglobulin E, and it assesses the correlation of the individual class scores of CAP and modified RAST with end points obtained from skin-dilutional end-point titration. The reproducibility of CAP was also assessed. Patients evaluated at the University of Chicago Allergy Clinic who had a history and physical examination consistent with immunoglobulin E–mediated allergy and in whom skin testing was clinically indicated as part of their allergy management, were asked to donate some blood for simultaneous in vitro testing by PhadezymRAST and ImmunoCAP. Testing was performed in batches. Random samples from the CAP batches were chosen for duplicate runs under conditions blinded to the technician. Receiver operating curve analysis was used for comparison of the sensitivity and specificity of RAST vs. that of CAP. We used Pearson product-moment correlation coefficients to compare the correlation of RAST and CAP classes with the end points from skin testing. Our results indicate that the sensitivity and specificity of RAST and CAP are similar, that the classes of these two tests correlate well with the end points from skin testing, and that duplicate samples of CAP also correlate well.