2019 Volume 68 Issue 3 Pages 514-518
We previously reported that the results of improved dimension tacrolimus (TAC) assay (Siemens), which is based on the affinity column-mediated immune assay (ACMIA), are affected by EDTA used as an anticoagulant. However, EDTA was improved as a reagent to EDTA-2K in 2018. In this study, we evaluated the analytical performance of the improved TAC assay using EDTA-2K in comparison with the conventional assay. In the EDTA interference study, the TAC concentration was decreased by 16.6% with 3.8 mg/mL EDTA-2K, corresponding to a half volume in the conventional assay, and the effect was observed in a concentration-dependent manner. However, the TAC concentration was decreased by only 1.4% with 3.8 mg/mL EDTA-2K in the improved assay. The within-run precisions obtained were 4.2% at a low concentration (mean: 3.9 ng/mL), 3.7% at a medium concentration (mean: 10.9 ng/mL), and 2.8% at a high concentration (mean: 20.9 ng/mL), which were equivalent to those of the conventional assay at each concentration. In addition, the limits of quantitation of the improved and conventional assays were determined to be 0.5 and 0.3 ng/mL, respectively, confirming that the measurement accuracy of the improved assay is higher than that of the conventional assay. In conclusion, it was revealed that in the improved assay, the effect of the EDTA concentration on the blood TAC concentration measurement was reduced in comparison with that in the conventional assay. The improved assay is useful for the routine TDM of TAC.
