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Clinical Chemistry 45: 1868-1870, 1999;
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(Clinical Chemistry. 1999;45:1868-1870.)
© 1999 American Association for Clinical Chemistry, Inc.

Technical Briefs

Comparison of Tacrolimus Concentrations Measured by the IMx Tacrolimus II vs the PRO-TRAC II FK506 ELISA Assays

Zhimin (Tim) Cao1, Mark W. Linder1,a, Anthony W. Jevans2, Glenda Brown1 and Roland Valdes Jr1

1 Department of Pathology and Laboratory Medicine, University of Louisville School of Medicine, Louisville, KY 40292;
2 Department of Pathology, Louisville Jewish Hospital, Louisville, KY 40202;
a author for correspondence: fax 502-852-1771, e-mail mwlind01@gwise.louisville.edu

Contemporary practice in the therapeutic monitoring of the immunosuppressant tacrolimus has required increasingly rapid and more sensitive assays. To this end, the two most commonly used immunoassay formats, IMx Tacrolimus II (Tacrolimus II) and PRO-TRAC IITM FK506 (ProTrac II) have undergone extensive revision, leading to changes in the measured drug concentration relative to the original assay format (1)(2)(3). Multiple studies have compared the original microparticle enzyme immunoassay (MEIA) and second-generation Tacrolimus II methods [e.g., Refs. (2)(3)], one report has compared the original MEIA and the second-generation ProTrac II method (1), and two preliminary reports have compared the ProTrac II method with the Tacrolimus II method (4)(5). In each of these reports, the ProTrac II method consistently yielded lower tacrolimus concentrations than the Tacrolimus II assay.

The aim of this study was to further characterize the correlation between the Tacrolimus II method and the ProTrac II ELISA.

Tacrolimus II controls were kindly provided by Abbott Laboratories (Abbott Park, IL). Pure tacrolimus powder was a courtesy of Fujisawa USA (Chicago, IL).

Tacrolimus stock solutions in whole blood at concentrations of 5.0, 10.0, and 20.0 µg/L were prepared from tacrolimus powder. Tacrolimus powder was initially dissolved in methanol, followed by sequential dilution with drug-free human whole blood. Tacrolimus assays were performed according to manufacturers instructions.

Correlation data were analyzed by Deming regression [Medsnap program (6)]. Differences between the two methods were analyzed by the methods of Bland and Altman (7)(8).

Fifty-five whole blood specimens from 39 transplant patients [heart (n = 9), lung (n = 9), kidney (n = 7), liver (n = 10), and bone-marrow (n = 4); human studies approval UHSC 35-97] were initially assayed for tacrolimus with the . . . [Full Text of this Article]


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