Specific Enzyme-Multiplied Immunoassay and Fluorescence Polarization Immunoassay for Cyclosporin Compared with Cyclotrac [125I]Radioimmunoassay

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Abstract
The analysis of cyclosporin-A (CsA) has proved a valuable adjunct to clinical care of patients who have received organ grafts. The measurement of CsA in whole blood by specific methods has recently taken a new direction with the introduction of a range of rapid methods, including a homogeneous enzyme immunoassay technique (EMIT) and a monoclonal fluorescence polarization immunoassay (FPIA). The present paper compares these two methods with the established Cyclotrac specific [125I]RIA (radioimmunoassay) using both commercial CsA-spiked control material as well as a group of 60 patient specimens (predominantly renal transplants). While each of the new methods showed acceptable precision and accuracy with the commercial quality control material, significant differences were demonstrated with patient specimens, such that FPIA was 12.5% greater than [125I]RIA (p less than 0.0001), which was in turn 5.9% greater than EMIT (p = 0.007). These data suggested that the FPIA may have residual CsA-metabolite interference and that the EMIT method was the most "specific" for parent CsA of the three tested, potentially therefore more comparable to high-performance liquid chromatography (HPLC).

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