Multi-center analytical evaluation of a novel automated tacrolimus immunoassay

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.

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.

Linearity from 0.5 to 40 μg/L was observed and functional sensitivity of 0.3 μg/L (CV ≤ 20%) was determined. Within-run imprecision was ≤ 5.1% on cobas e 602 (5.1% at 1.5 μg/L) and ≤ 8.9% (8.9% at 0.8μg/L) on cobas e 411. The intermediate imprecision for TAC concentrations ≥ 6.8 μg/L was ≤ 6.5%. At lower therapeutic concentrations (to 1.5 μg/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.

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.