Assay of vancomycin by fluorescence polarisation immunoassay and EMIT in patients with renal failure.

Serum with vancomycin concentrations between 5 and 15 mg/L from patients on dialysis were assayed by fluorescence polarization immunoassay (FPIA) and enzyme multiplied immunoassay technique (EMIT). The concentrations as determined by FPIA were higher than those using EMIT (mean difference 2.1 mg/L, S.D. 1.5; range -0.8-6.3) with substantial interpatient variability in the difference between the two assays. This suggests that concentrations of active vancomycin are lower than indicated by FPIA and thresholds for redosing may need to be adjusted.