Commentary Note: Do We still Need Liquid Chromatography Combined with Mass Spectrometry for Therapeutic Drug...

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.

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.

From February 2, 2023, till November 18^th, 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%.

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