Commentary Note: Do We still Need Liquid Chromatography Combined with Mass Spectrometry for Therapeutic Drug Monitoring of Tacrolimus?

OBJECTIVE

In our laboratory, chemiluminescent microparticle immunoassay (CMIA) of tacrolimus on the Alinity i was implemented in February 2023 with an option for physicians to request liquid chromatography combined with mass spectrometry (LC-MS/MS) analysis to confirm the level of the immunoassay result.

METHODS

CMIA tacrolimus was performed on the Alinity i analyzer and the result was reported within 4h. However, if a physician requested LC-MS/MS analysis, the same whole blood specimen was sent to the reference laboratory, where the result was available within 24h. We then compared the LC-MS/MS value with the initial immunoassay result, which was performed in the same specimen.

RESULTS

From February 2, 2023, till November 18th, 2025, 51,833 tacrolimus tests were ordered in our laboratory. Out of all these specimens only 795 specimens (1.53%) were sent to the reference laboratory for further analysis by LC-MS/MS as requested by ordering physicians. In the majority of specimens (634 out of 795, 79.7%) difference between immunoassay and LC-MS/MS was less than 20%. However, 27 specimens (3.4%) showed positive bias over 30% with a highest bias of 76.7%.

CONCLUSION

LC-MS/MS is still needed for therapeutic drug monitoring of tacrolimus.