Performance of a no-pretreatment tacrolimus assay on the Dade Behring Dimension RxL clinical chemistry analyzer

Background: Therapeutic drug monitoring for tacrolimus is important for organ transplant patients receiving this immunosuppressant. Current available assays for tacrolimus require sample pre-treatment and operate in a batch mode. Here a no-pretreatment tacrolimus assay, performed on the Dade Behring Dimension analyzer is compared to the Abbott IMx tacrolimus assay and to an LC/MS/MS method. Methods: Whole blood samples from 2 medical centers and different transplant types (kidney n = 104, liver n = 84, heart n = 28, pancreas n = 16, bone marrow n = 11, lung n = 7), were obtained and tacrolimus quantified by each of the 3 assays. Results: The lower limit of the linear range was 1.2 ng/ml on the Dimension assay. Total imprecision was 9.8% and within-run imprecision was 9.6% at a tacrolimus concentration of 3.4 ng/dL. Passing-Bablock regression analysis determined the following relationships: DIMN = (1.16) LC/MS - 0.43, r = 0.90 and DIMN = (0.99)IMx - 0.35, r = 0.87. Conclusions: The Dade Behring Dimension II Tacrolimus assay has adequate imprecision and correlates well with the reference method of LC/MS/MS. The assay appears suitable for clinical use, and has the advantages of not requiring a pretreatment step and the ability to be performed in a random-access mode.