Laboratory evaluation of five assay methods for vancomycin: bioassay, high-pressure liquid chromatography, fluorescence polarization immunoassay, radioimmunoassay, and fluorescence immunoassay.

We compared the precision and accuracy of five methods used to measure the concentration of vancomycin in serum: bioassay, high-pressure liquid chromatography, fluorescence polarization immunoassay (FPIA [TDX; Abbott Laboratories, North Chicago, Ill.]), radioimmunoassay (RIA), and fluorescence immunoassay. Based on an analysis of seven standards and of 106 patient samples, all five methods were accurate, and four (bioassay, high-pressure liquid chromatography, FPIA, and RIA) were also precise. The FPIA was the most precise and the fluorescence immunoassay was the least precise of the methods tested; intrarun coefficients of variation for these two methods were 0.9 to 3.0% versus 8.9 to 14.5%, and interrun coefficients of variation were 2.8 to 8.1% versus 12.2 to 16.2%, respectively. The RIA was inconvenient because it required an extra dilution of the specimen being tested and an additional (64 micrograms/ml) vancomycin standard for specimens with 32 to 64 micrograms of vancomycin per ml. Based on its rapid turnaround time and the stability of its standard curve, we believe that the FPIA is the best method currently available to quantitate vancomycin in the clinical laboratory.