Evaluation of the New Siemens Tacrolimus Assay on the Dimension EXL Integrated Chemistry System Analyzer: Comparison With an Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry Method.

BACKGROUND: Many patients are maintained at the lower end of the tacrolimus (TAC) reference range (3-7 ng/mL), requiring the use of analytical methods displaying a very low limit of quantification for their follow-up. Therefore, the new Dimension TAC, based on affinity chrome-mediated immunoassay technology, was evaluated on the Dimension EXL Integrated Chemistry System (Siemens Healthcare Diagnostics Inc). The aims of this study were (1) to evaluate the analytical performances with special emphasis on sensibility at low levels of TAC, (2) to compare the results with an ultra-performance liquid chromatography-tandem mass spectrometry (UPLC/MS/MS) method.

METHODS: Analytical performance (imprecision, linearity, limit of detection, and limit of quantification) was evaluated. Comparison to UPLC/MS/MS was performed on 106 whole blood samples from 88 transplant recipients using regression analysis and Bland-Altman plot analysis.

RESULTS: Repeatability and within-laboratory coefficients of variation were <6% at mean TAC control levels of 3.7, 11.7, and 19.2 ng/mL. Linearity was confirmed between 1.0 and 22 ng/mL. Passing-Bablok regression analysis of Siemens TAC assay in comparison with UPLC/MS/MS values displayed a slope of 1.09 and an intercept of -0.42. Using Bland-Altman analysis, the mean bias was 0.27 ng/mL with 1.96 SD limits of -2.14 and 2.67 ng/mL.

CONCLUSIONS: The new Dimension TAC immunoassay on the EXL analyzer demonstrated reliable and reproducible performances allowing routine monitoring in transplant patients, even at TAC concentrations at the lower end of the therapeutic range.