Long-term accuracy of fluorescence polarization immunoassays for gentamicin, tobramycin, netilmicin and vancomycin

External quality control was performed during six years to determine the accuracy over time of the Abbott TDx fluorescence polarization system for assaying antibiotics. Unknown spiked serum samples of gentamicin, tobramycin, netilmicin and vancomycin were provided monthly by the British national external quality assessment scheme. Comparison of the 209 assay results with the target concentrations showed good correlations in all four assays. No significant deviations from linearity, from slope 1.0, and from intercept 0.0 were detected by regression analysis. Relative deviations were less than 10% and less than 15% for 78% and 90% of all specimens, respectively. On an average the same calibration curves could be used over a period of 19 weeks. Fluorescence polarization immunoassays provided rapid and reliable results over the entire study period.