Is the automated Elecsys tacrolimus assay on the Roche cobas e 602 analyzer an acceptable replacement for a liquid chromatography-tandem mass spectrometry-based assay?

Objectives: This study evaluated the suitability and accuracy of the automated Roche Elecsys tacrolimus electrochemiluminescence immunoassay (ECLIA) by comparing it with a current laboratory-developed test by liquid chromatography-tandem mass spectrometry (LC-MS/MS).Methods: The tacrolimus ECLIA was evaluated for precision, linearity, interference, and postextraction stability. Accuracy was compared with LC-MS/MS.Results: The tacrolimus ECLIA assay is precise, exhibits a measuring range of 0.75 to 30 ng/mL, and is tolerant of significant interferences (plasma indices: hemolysis <2306, icterus <55, lipemia <1427, and biotin <1200 ng/mL). Comparison with LC-MS/MS revealed a 26% proportional bias in patient samples evaluated for tacrolimus concentration (y = 1.26x + 0.08; r(2) = 0.97; Sy/x = 0.94; n = 43) and an absolute mean (SD) bias of 2.2 (1.7) ng/mL. Postextraction studies confirmed that samples were stable for up to 30 minutes under routine laboratory conditions.Conclusions: The 2 major challenges for implementation of the tacrolimus ECLIA assay are the postextraction sample stability and the significant proportional bias observed compared with the LC-MS/MS reference method. The 30-minute window for analysis of extracted samples is a practical challenge to the routine workflow of the core laboratory. In addition, disagreement between the immunoassay and LC-MS/MS methods can lead to discordant clinical interpretations and ultimately affect patient care.