Evaluation of the tacrolimus II microparticle enzyme immunoassay (MEIA II) in liver and renal transplant recipients.

We evaluated the MEIA II with blood samples with added tacrolimus (3.0, 5.0, 11.0, and 22.0 microg/L). The assay had acceptable recoveries (99-103%) and intraday imprecision (<16.0%) across the range of concentrations studied, except for the recoveries at 3.0 microg/L (86.3%) and 5.0 microg/L (80.7%). Comparison of liver (n = 116) and renal (n = 113) patient samples measured by MEIA II against HPLC-tandem mass spectrometry (HPLC-MS/MS) found a mean overestimation of 15.6%. From these comparison data it can be calculated that at values of 5 and 20 microLg/L in liver or renal transplant patient samples, measured by HPLC-MS/MS, MEIA II will have the corresponding range estimates of 3.6-7.9 microg/L and 20.9-25.4 microg/L, respectively. No clinically significant difference in results, in terms of overestimation or correlation, was observed between the two transplant groups studied. The MEIA II is an improvement on the previous MEIA I and is suitable for the therapeutic drug monitoring of tacrolimus where HPLC-MS/MS is unavailable.