NEW MODIFIED FLUORESCENCE POLARIZATION IMMUNOASSAY DOES NOT FALSELY ELEVATE VANCOMYCIN CONCENTRATIONS IN PATIENTS WITH END-STAGE RENAL-DISEASE

Recent literature has urged caution in the interpretation of vancomyci n serum concentrations in patients with end-stage renal disease (ESRD) , because falsely elevated levels in excess of 70% have been reported with the most commonly used fluorescence polarization immunoassay (FPI A). The purpose of this study was to evaluate the performance of a rec ently modified FPIA assay for use in patients with ESRD, in comparison to high-performance liquid chromatography (HPLC) and an enzyme-mediat ed immunoassay technique (EMIT). Serum vancomycin samples were prospec tively collected from adults with ESRD undergoing chronic hemodialysis . Each sample was stored at -70 degrees C until analyzed in duplicate by FPIA, EMIT, and HPLC. In an in vitro experiment, blank serum sample s with 15 mu g/ml vancomycin were spiked with increasing amounts of CD P and analyzed in duplicate with the modified FPIA assay. When compare d to HPLC, no statistically significant difference was found in patien ts with ESRD with the use of the modified FPIA assay (mean concentrati ons, HPLC 14.92 mu g/ml, FPIA 15.96 mu g/ml), with FPIA exhibiting a p ositive bias of 0.64 mu g/ml and a precision of +/-3.49 mu g/ml (n = 1 8, p = 0.44). The mean EMIT concentration was 18.34 mu g/ml, with a po sitive bias of 3.43 mu g/ml and a precision of +/-5.17 mu g/ml (p < 0. 01). The addition of increasing amounts of CDP to vancomycin in vitro resulted in concentrations similar to those expected in the absence of significant cross-reactivity with the modified FPIA assay. The modifi ed FPIA assay is a satisfactory tool for monitoring vancomycin serum c oncentrations in patients with ESRD undergoing hemodialysis. Results o btained with EMIT were not as precise as with FPIA.