Measurement of Whole Blood Tacrolimus Level by High Performance Liquid Chromatography Tandem Mass Spectrometry in Renal Transplant Recipients — A Single Center Perspective

Background and Methods Measurement of whole blood tacrolimus level by high performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) was compared with that measured by microparticle enzyme immunoassay (MEIA) in 30 renal transplant recipients. Results Whole blood tacrolimus concentrations measured by HPLC-MS/MS were significantly lower than those measured by MEIA, with a median difference (interquartile range, IQR) of −0.40 μg/L (2.03 μg/L) ( p r = 0.94; p 12 ) of tacrolimus derived using the two-point sampling equation with tacrolimus concentrations measured by HPLC-MS/MS was compared with that measured by MEIA. The AUC 12 values calculated by the two methods were highly correlated ( r = 0.90; p 12 values was 3.4 ± 11.6 hr.μg/L, and the mean percentage difference was 2.6 ± 11.4%, both of which were not statistically significant. Conclusion For tacrolimus concentrations within the recommended therapeutic range, the concentration measured by HPLC-MS/MS was statistically significantly lower than that measured by MEIA, but the difference was not clinically significant. Introduction of the more specific HPLC-MS/MS method does not require adjustment in the recommended tacrolimus trough concentration or the AUC 12 level estimated by our abbreviated regression equation.