Determination of tacrolimus in human whole blood in kidney transplant recipients using a rapid and specific LC–MS/MS method

Abstract Objective To develop and validate an LC‐M/SMS method for the determination of tacrolimus in human whole blood. Method The LC–MS/MS method for the determination of tacrolimus in whole blood was developed and validated according to the guidelines. Concentrations of TAC in 100 kidney transplant patients measured by LC–MS/MS were compared with CMIA using correlation analysis and Bland–Altman plots. Results The method had a total chromatographic run time of 5 min. The calibration curves were linear over the range of 0.5–100.0 ng/mL with a lower limit of quantification of 1 ng/mL. The intra‐ and interday accuracy was within the range of 93.3%–109.2% and 96.0%–108.4%, respectively, with precision ranging from 0.8 to 9.4%. The mean extraction recoveries of TAC ranged from 102.6 to 107.8%. The mean concentrations of TAC in whole blood of kidney transplant patients measured by the two assays were different at 1, 3 months and all time points ( p < 0.001), but no significant difference was observed at 6 months ( p = 0.094). The correlation of data was good with the correlation coefficients ( r 2 ) of 0.7581, 0.8811, 0.8777, and 0.8077, respectively. Passing–Bablok regression analysis demonstrated good correlations with r 2 values higher than 0.88 between TAC levels measured by LC–MS/MS and CMIA. Using Bland–Altman plots yielded average biases of 1.29, 0.79, 0.11, and 0.65 ng/mL at 1, 3, and 6 months and all time points. Conclusion The LC–MS/MS method was validated for the accurate determination of TAC in human whole blood. The comparison of tacrolimus concentrations measured by the LC–MS/MS with CMIA showed a good correlation and agreement of two methods, suggesting LC–MS/MS should be used routinely to monitor TAC concentrations in kidney transplant patients.