Multi-center analytical evaluation of a novel automated tacrolimus immunoassay

Background: Tacrolimus (TAC) is a post-transplantation immunosuppressant drug used in patients for whom careful monitoring of TAC concentration is essential. A new semi-automated immunoassay for TAC measurement, the Elecsys Tacrolimus assay, is available and has been assessed in a multi-center evaluation. Methods: Residual whole blood samples from patients undergoing TAC therapy after organ transplant were used in assay evaluation at five clinical laboratories in Europe. Experiments included imprecision according to CLSI EP5-A2 (within-run and intermediate), functional sensitivity, linearity according to CLSI EP6-A, and recovery from external quality assessment scheme (EQAS) samples. The assay was compared to LC-MS/MS used routinely at each investigational site, and to the Abbott Architect immunoassay. Results: Linearity from 0.5 to 40 mu g/L was observed and functional sensitivity of 0.3 mu g/L (CV <= 20%) was determined. Within-run imprecision was <= 5.1% on cobas e 602 (5.1% at 1.5 mu g/L) and <= 8.9% (8.9% at 0.8 mu g/L) on cobas e 411. The intermediate imprecision for TAC concentrations >= 6.8 mu g/L was <= 6.5%. At lower therapeutic concentrations (to 1.5 mu g/L) it was consistently <= 10%. Deming regression analysis of method comparison to LC-MS/MS yielded slopes of 1.07 (95% CI: 1.05/1.10) for heart transplant samples, 1.13 (95% CI: 1.09/1.16) for kidney, and 1.05 (95% CI: 1.02/1.08) for lung transplant samples. Conclusions: The Elecsys Tacrolimus assay has good linearity, functional sensitivity and intermediate imprecision and is comparable to LC-MS/MS methods. The over-all performance of ECLIA demonstrates a modern generation TAC assay that meets the demands of monitoring drug concentrations in current immunosuppressive regimens.

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