Inter-laboratory variability of current immunoassay methods for tacrolimus among Japanese hospitals

The aim of this study was to assess inter-hospital laboratory variability (coefficient of variation; CV) of immunoassay methods for tacrolimus and the comparability of control samples and results obtained by immunoassay measurements. One hundred seven hospital laboratories routinely performing therapeutic drug monitoring (TDM) of tacrolimus participated in the study. Thirteen spiked samples with known tacrolimus concentrations in the range of 0-26.0 ng/mL were prepared. Each spiked sample was analyzed according to the manufacturer's instructions using an affinity column-mediated immunoassay (ACMIA) on a Dimension® analyzer, the enzyme multiplied immunoassay technique (EMIT) on a Viva-E® analyzer, a chemiluminescent enzyme immunoassay (CLIA) on the Architect® system, and the electro-chemiluminescence immunoassay (ECLIA) on a cobas® analyzer. The 20% coefficient of variation values for the CLIA, ACMIA, EMIT, and ECLIA assays in the hospital laboratories were 1.82, 5.36, 4.59, and 0.89 ng/mL, respectively. CLIA and ECLIA had positive biases at concentrations of tacrolimus above 12 ng/mL relative to the spiked concentration, whereas the assay bias for ACMIA tended to be more negative at concentrations of tacrolimus above 6 ng/mL. EMIT had positive biases over the wide concentration range of 0.0-26.0 ng/mL (mean of mean errors 1.224). CLIA and ECLIA provided adequate precision at the target tacrolimus concentration of 3.0 ng/mL, whereas ACMIA and EMIT were unable to respond to target concentrations between 3.0 and 5.0 ng/mL for renal transplant recipients. Appropriate assessment of tacrolimus concentration by an assay having higher sensitivity, precision, and accuracy is necessary to ensure long-term survival of transplant recipients receiving tacrolimus.