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Three commercial polyclonal immunoassays for cyclosporine in whole blood compared: 1. Results with patients'
M J Strassman1, G L Lensmeyer, D A Wiebe
1Department of Pathology and Laboratory Medicine, University of Wisconsin Hospital & Clinics, Madison 53792.
Insights
Commercial cyclosporine (CsA) immunoassays show significant variability in whole-blood measurements. Patient results are not interchangeable between different assay methods, impacting clinical interpretation.
Area of Science:
- Clinical Chemistry
- Pharmacology
- Immunology
Background:
- Cyclosporine (CsA) is a critical immunosuppressant medication used in organ transplantation.
- Accurate monitoring of CsA whole-blood concentrations is essential for therapeutic efficacy and preventing toxicity.
- Several commercially available immunoassays exist for CsA measurement, but their performance characteristics may vary.
Purpose of the Study:
- To evaluate and compare the performance of three commercially available polyclonal immunoassays for apparent cyclosporine (CsA) in whole blood.
- To assess the interchangeability of CsA results obtained from different immunoassay methods.
- To investigate the impact of CsA metabolites on assay accuracy and inter-method variability.
Main Methods:
- Analyzed 120 whole-blood specimens from transplant recipients using Abbott TDx (fluorescent polarization immunoassay), Sandoz RIA, and Incstar Cyclo-Trac RIA.
- Determined mean coefficients of variation (CVs), analytical recovery, and linearity for each assay.
- Quantified parent CsA concentrations using High-Performance Liquid Chromatography (HPLC) for comparison.
- Assayed serial specimens from six patients to track day-to-day fluctuations and inter-method agreement.
Main Results:
- Mean CVs varied significantly across the assays: 3.8% (Abbott), 9.3% (Sandoz), and 24.3% (Incstar).
- Analytical recovery was high for lower concentrations but linearity was compromised at higher levels (>1000-1500 µg/L).
- Methods showed dissimilar but parallel results, with occasional deviations from established trends, partly due to cross-reactivity with CsA metabolites.
- HPLC analysis confirmed discrepancies among immunoassay results.
Conclusions:
- Commercially available polyclonal immunoassays for apparent cyclosporine demonstrate significant performance differences.
- Interchangeability of patient results between these methods is not reliable due to assay biases and cross-reactivity with metabolites.
- Clinical decisions based on cyclosporine levels should consider the specific assay method used.
Abstract:
We assessed the performance of three commercially available polyclonal immunoassays for apparent cyclosporine in 120 whole-blood specimens collected from transplant recipients just before their next dose of cyclosporine (CsA). The assays were (a) Abbott's TDx fluorescent polarization immunoassay for CsA and its metabolites in whole blood; (b) the Sandoz radioimmunoassay (RIA); and (c) Incstar's Cyclo-Trac RIA. Mean respective CVs were 3.8%, 9.3%, and 24.3%. Analytical recovery was nearly 100% for concentrations up to 1000 micrograms/L for Incstar and up to 1500 micrograms/L for Abbott and Sandoz; linearity was compromised at greater concentrations. We also quantified the parent CsA concentrations by HPLC. Moreover, to follow day-to-day fluctuations in patients' "cyclosporine" concentrations with each method and to assess the impact these differences have on interpretation of the analytical results, we assayed serial specimens from six post-transplant patients. These showed significantly dissimilar, but parallel, results among the methods for any single sample. Occasionally, however, a result would not fit the established trend. Biases observed among the assays can be explained in part by the nonspecific antisera cross-reacting with CsA metabolites. Most important, we demonstrate that patients' results are not reliably interchangeable among the methods.