Standardization of LC-MS for Therapeutic Drug Monitoring of Tacrolimus

Importance of the Topic

The immunosuppressant tacrolimus is a cornerstone in preventing organ rejection after transplantation, yet its narrow therapeutic window and high interpatient variability demand precise therapeutic drug monitoring (TDM). Standardized, traceable assays ensure consistent dosing decisions and patient safety across clinical laboratories.

Objectives and Study Overview

This study evaluated whether using the commercial MassTrak Immunosuppressants Kit on the Waters ACQUITY TQD platform improves interlaboratory precision for tacrolimus TDM. Seven laboratories in the USA and Europe participated in a proficiency-testing survey. Results were compared against an established in-house LC-MS method and a higher-order reference measurement procedure (RMP).

Methodology and Instrumentation

A proficiency panel of 10 patient-derived whole blood pools and 10 tacrolimus-spiked samples (0–25 ng/mL) was prepared in duplicate (n=40). Samples were randomized and analyzed blindly following the kit’s sample pretreatment protocol. Data analysis included calculation of interlaboratory coefficient of variation (CV), Passing–Bablok regression, Pearson correlation, and Bland–Altman bias estimation.

Used Instrumentation

• Waters ACQUITY TQD LC-MS/MS system
• MassTrak Immunosuppressants Kit
• MassLynx Software
• Certified calibration vials

Main Results and Discussion

For spiked samples, interlaboratory CV ranged from 3.7% to 12.2%; for patient pools, CV ranged from 2.0% to 5.4% (mean 4.3%). Overall mean CV was 5.5%, improved over the 6.4% mean CV reported for an Abbott Architect immunoassay. The MassTrak assay demonstrated excellent agreement with the in-house LC-MS method (Passing–Bablok: y=1.02x–0.02; r=0.99) and with the RMP, with biases ≤4.4% across the therapeutic range.

Benefits and Practical Applications of the Method

• High reproducibility and consistency across multiple laboratories
• Traceability to higher-order reference procedures ensuring accuracy
• Reduced interference from metabolites, hematocrit variations, and heterophilic antibodies compared to immunoassays
• Seamless integration into routine clinical TDM workflows

Future Trends and Possibilities

Expansion of standardized LC-MS assays to additional immunosuppressants; integration with automated sample preparation systems; development of digital quality control frameworks; and application of AI-driven data analytics to enhance assay robustness and laboratory efficiency.

Conclusion

Standardizing tacrolimus LC-MS analysis via a commercial kit and common platform yields precise, accurate, and traceable TDM results, representing a significant advancement over both immunoassays and laboratory-developed tests.

Reference

1. Wallemacq P, et al. Therapeutic Drug Monitoring. 2009;31:139–152.
2. Bouamar R, et al. American Journal of Transplantation. 2013;13:1253–1261.
3. Levine DM, et al. Clinical Chemistry. 2011;57:1739–1747.
4. Napoli KL, et al. Clinical Biochemistry. 2010;43:910–920.
5. Staatz CE, Taylor PJ, Tett SE. Therapeutic Drug Monitoring. 2002;24:607–615.
6. Napoli KL. Therapeutic Drug Monitoring. 2006;28:491–504.
7. Brown NW, et al. Clinical Chemistry. 2005;51:586–592.
8. Taylor PJ, Morris RG. Therapeutic Drug Monitoring. 2003;25:259–260.
9. Altinier S, et al. Clinica Chimica Acta. 2009;402:193–195.