Vancomycin assay performance in patients with acute renal failure

Objective: Fluorescence polarization immunoassays (FPIA) have been reported to overestimate vancomycin serum concentrations compared to high-performance liquid chromatography (HPLC) or enzyme multiplied immunoassay technique (EMIT) in patients with chronic renal disease. The assay manufacturer has modified the FPIA to remedy this overestimation. The purpose of this study was to compare the assay performance of two FPIAs to EMIT in acute renal failure patients receiving vancomycin and continuous venovenous hemofiltration.¶Design: Open-label trial.¶Setting: Intensive care unit in a university affiliated hospital.¶Patients and participants: 15 serum and ultrafiltrate samples were obtained from 14 critically ill patients (mean ± SD; 57 ± 12 years; 8 males/6 females).¶Measurements and results: Vancomycin concentrations were determined by a polyclonal FPIA (pFPIA) performed on the TDx system, a monoclonal FPIA (mFPIA) performed on the AxSYM system and EMIT. The coefficient of variation for all assays was < 5 %. The mean difference ± SD_d between mFPIA vs EMIT and pFPIA vs EMIT assays in serum were: –0.08 ± 1.55 and 1.24 ± 2.11 mg/l, respectively. The limits of agreement between the mFPIA vs EMIT and pFPIA vs EMIT assays in serum were: –3.18 to 3.03 and –2.99 to 5.46 mg/l, respectively.¶Conclusions: Our data demonstrate that the manufacturer's changes to the pFPIA have reduced overestimation. The mFPIA appears to be an acceptable assay for measuring vancomycin serum concentrations in acute renal failure patients and does not significantly overestimate these concentrations.