New liquid chromatography-tandem mass spectrometry method for routine TDM of vancomycin in patients with both normal and impaired renal functions and comparison with results of polarization fluoroimmunoassay in light of varying creatinine concentrations

The results obtained with LC-MS/MS method were correlated with an FPIA assay (Abbott AxSYM) using mouse monoclonal antibody. Subjects were divided into three groups according to creatinine levels (53.5 ± 19.1, 150.2 ± 48.4, 471.7 ± 124.7 μmol/L) and Passing-Bablok regression analysis and Bland-Altman analysis were used to compare vancomycin concentrations. The results of subjects with both normal and higher creatinine levels correlated very well and the linear regression model equations were near ideal (LC-MSVAN = 0.947 × AbbottVAN + 0.192 and LC-MSVAN = 0.973 × AbbottVAN − 0.411 respectively). Dialyzed patients with the highest creatinine levels showed about 14% greater vancomycin concentration with the FPIA assay (LC-MSVAN = 0.866 × AbbottVAN + 2.127). This overestimation probably due to the presence of the metabolite CDP ought not to be of clinical relevance owing to the wide range of recommended vancomycin concentration.