Evaluation of the Waters MassTrak LC–MS/MS Assay for Tacrolimus and a Comparison to the Abbott Architect Immunoassay

BackgroundTacrolimus (Prograf, Advagraf, and FK-506) is the most commonly prescribed calcineurin inhibitor after kidney and liver transplantation. The use of tacrolimus (in conjunction with other drugs) has successfully contributed to the maintenance of solid organ allografts; however, it also exhibits toxic side effects. Therapeutic drug monitoring of tacrolimus is used as an aid to achieve drug concentrations within a narrow therapeutic window.MethodsThe Waters MassTrak Immunosuppressants assay (LC-MS/MS) for the quantification of tacrolimus in whole blood was evaluated for precision, linearity, lower limit of quantification, matrix effects, and accuracy. A method comparison with the Abbott Architect Tacrolimus immunoassay was also performed.ResultsThe mean concentration (nanograms per milliliter) and coefficient of variation for low, mid, and high patient pools were 0.6% ± 19.9%, 16.0% ± 5.4%, and 31.2% ± 5.8%, respectively. The MassTrak assay was linear from 0.5 to 30.0 ng/mL. Although the MassTrak and Architect assays correlated well (R = 0.97) for patient samples, the MassTrak assay displayed an average negative bias of 18.5% versus Architect (range of 0.0%-36.7%). Analysis of a certified tacrolimus reference material in human whole blood [European Reference Materials (ERM)-DA110a, LGC Standards] on both platforms failed to completely explain the observed difference for patient samples.ConclusionsTwo widely used assays for therapeutic drug monitoring of tacrolimus are not in agreement with one another. Care should be exercised when interpreting results generated on these 2 assay platforms