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BRIEF RESEARCH REPORT article

Front. Transplant.

Sec. Immunosuppression

Comparative Evaluation of Five Tacrolimus Assays in Transplant Recipients: Implications for Optimizing Therapeutic Drug Monitoring

Provisionally accepted
Ivo N. SahBandarIvo N. SahBandar1Zhen ZhaoZhen Zhao2Sabrina E. Racine-BrzostekSabrina E. Racine-Brzostek2Alex J. RaiAlex J. Rai3Maria CidMaria Cid1Melissa M. CushingMelissa M. Cushing2Neal LindemanNeal Lindeman2Thangamani MuthukumarThangamani Muthukumar1He Sarina YangHe Sarina Yang2*
  • 1NewYork-Presbyterian Weill Cornell Medical Center, New York, United States
  • 2Weill Cornell Medicine, New York, United States
  • 3New York-Presbyterian/Columbia University Irving Medical Center, New York, United States

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Tacrolimus is a widely used immunosuppressive therapy in transplant recipients, but its narrow therapeutic index necessitates accurate monitoring. Tacrolimus levels can be quantified using immunoassays (IAs) and liquid chromatography-tandem mass spectrometry (LC-MS/MS), however differences between these methods may influence clinical decision-making. In this study, we compared two IAs, i.e. chemiluminescent (CMIA) and electrochemiluminescent (ECLIA), with three LC-MS/MS assays in 181 clinical specimens. When compared with the overall mean concentration, all five assays showed strong correlations, though with variability across methods: three LC-MS/MS assays demonstrated correlation coefficients of 0.9927, 0.9612, and 0.9920, while two immunoassays yielded coefficients of 0.9938 and 0.9857. Deming regression analysis revealed slopes of 0.96, 0.94, and 0.93 for the three LC-MS/MS, while the immunoassays showed higher slopes of 1.032 (ECLIA) and 1.21 (CMIA). Bland–Altman analysis indicated systematic underestimation by the LC-MS/MS methods (–7.5%, –18.7%, and –8%) and overestimation by the immunoassays (ECLIA +9.7%, CMIA +18.4%), relative to the overall mean. The two immunoassays showed only moderate agreement with each other (slope = 0.85, intercept = 0.49), and even the LC-MS/MS assays were not fully concordant. Among 47 patients within 3 months post-transplantation and 134 patients beyond 3 months, clinically relevant discrepancies (≥2 ng/mL) between LC-MS/MS and immunoassay results were observed in 13 patients (28%) and 49 patients (37%), respectively. These findings underscore the substantial impact of assay-dependent variability on tacrolimus monitoring

Keywords: Tacrolimus, Therapeutic drug monitoring, Immunoassay, Mass Spectrometry, Transplant recipients

Received: 30 Sep 2025; Accepted: 13 Nov 2025.

Copyright: © 2025 SahBandar, Zhao, Racine-Brzostek, Rai, Cid, Cushing, Lindeman, Muthukumar and Yang. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: He Sarina Yang, hey9012@med.cornell.edu

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

Supplementary Material