TAC Assays Research Articles

The EMIT 2000 tacrolimus assay: an application protocol for the Beckman Synchron LX20 PRO analyzer

Objective: To develop and evaluate the performance of an application protocol for the EMIT 2000 tacrolimus (Tac) assay on the Beckman Synchron LX20 PRO Analyzer. Design and Methods: Precision, accuracy, linearity, and lower limit of quantitation were investigated. Specimens from 212 kidney, liver, heart/heart–lung, and islet cell transplant patients were analyzed and results were compared to those from the Abbott MEIA II assay. A separate population of 232 specimens was coanalyzed by the enzyme-multiplied immunoassay technique (EMIT) assay and liquid chromatography tandem mass spectrometry (LC-MS/MS). Results: Total imprecision was 13.7% and 6.0% at concentrations of 3.4 and 19.1 μg/L, respectively. Recoveries from assayed reference materials ranged from 103% to 109%. A quantitation range of 3.2–30.0 μg/L was validated. The EMIT assay on the LX20 PRO analyzer showed an average negative bias of 1% compared to the MEIA assay and an average positive bias of 17% compared to LC-MS/MS. Conclusion: This application for the EMIT 2000 Tac assay on the Beckman Synchron LX20 PRO analyzer enhances the versatility of the immunoassay for routine therapeutic drug monitoring (TDM) of this immunosuppressant in the clinical setting.

Thiols as major determinants of the total antioxidant capacity.

The proper functioning of aerobic organisms subjected to the danger of uncontrolled oxidation depends critically on the efficient antioxidant system. This system includes antioxidant enzymes, low-molecular weight antioxidants and biological chelators of transition metal ions. What is an antioxidant? According to the apparently most useful definition, antioxidant is “any substance that, when present at low concentrations compared with those of an oxidizable substrate, significantly delays or prevents oxidation of that substrate” [1]. The usefulness of this definition lies, i. a., in its instrumentality as it suggests straightforward means of testing antioxidant properties of chemical compounds. In fact, testing the delay or inhibition of a chosen oxidation reaction allows for a simple measurement of the sum of all antioxidants present in the sample studied. This parameter is usually referred to as Total Antioxidant Activity or, as recommended lately, Total Antioxidant Capacity [2]. Total Antioxidant Capacity is an increasingly frequently measured parameter. While lacking detailed information about the composition and concentrations of individual antioxidant species present in a sample, it provides an easy and rapid means of evaluation of “antioxidant power” of the examined material. An obvious field of application of TAC assay is analysis of plants, food products and beverages. However, there are many attempts to apply this analysis for evaluation of antioxidant status of body fluids (especially blood plasma) in normal human subjects and animals. For research purposes, it is also of interest to evaluate TAC of cells and tissue homogenates in animals subjected to different treatments. There are numerous methods of estimating TAC. One group of methods is based on the inhibition of free-radical induced oxidation of an indicator compound or of a substrate yielding an indicator [3–5]. The