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Licensed Unlicensed Requires Authentication Published by De Gruyter February 14, 2013

Comparative evaluation of the My5-FU™ immunoassay and LC-MS/MS in monitoring the 5-fluorouracil plasma levels in cancer patients

Barbara Büchel , Johanna Sistonen , Markus Joerger , Yolanda Aebi , Stefan Schürch and Carlo R. Largiadèr EMAIL logo


Background: Chemotherapies of solid tumors commonly include 5-fluorouracil (5-FU). With standard doses of 5-FU, substantial inter-patient variability has been observed in exposure levels and treatment response. Recently, improved outcomes in colorectal cancer patients due to pharmacokinetically guided 5-FU dosing were reported. We aimed at establishing a rapid and sensitive method for monitoring 5-FU plasma levels in cancer patients in our routine clinical practice.

Methods: Performance of the Saladax My5-FU™ immunoassay was evaluated on the Roche Cobas® Integra 800 analyzer. Subsequently, 5-FU concentrations of 247 clinical plasma samples obtained with this assay were compared to the results obtained by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and other commonly used clinical analyzers (Olympus AU400, Roche Cobas c6000, and Thermo Fisher CDx90).

Results: The My-FU assay was successfully validated on the Cobas Integra 800 analyzer in terms of linearity, precision, accuracy, recovery, interference, sample carryover, and dilution integrity. Method comparison between the Cobas Integra 800 and LC-MS/MS revealed a proportional bias of 7% towards higher values measured with the My5-FU assay. However, when the Cobas Integra 800 was compared to three other clinical analyzers in addition to LC-MS/MS including 50 samples representing the typical clinical range of 5-FU plasma concentrations, only a small proportional bias (≤1.6%) and a constant bias below the limit of detection was observed.

Conclusions: The My5-FU assay demonstrated robust and highly comparable performance on different analyzers. Therefore, the assay is suitable for monitoring 5-FU plasma levels in routine clinical practice and may contribute to improved efficacy and safety of commonly used 5-FU-based chemotherapies.

Corresponding author: Carlo R. Largiadèr, Institute of Clinical Chemistry, Inselspital, Bern University Hospital, and University of Bern, INO-F, 3010 Bern, Switzerland, Phone: +41 31 632 95 45, Fax: +41 31 632 48 62

The My5-FU assay reagents, calibrators, pooled plasma samples for validation, 50 clinical plasma samples, and data for a subset of samples (AU400, CDx90, Cobas c6000) for method comparison were kindly provided by Saladax Biomedical. We thank J. Dias and U. Sonnenschein for their support in the My5-FU assay evaluation and P. Rhyn and C. Bühr for their expertise and help with the LC-MS/MS analyses.

Conflict of interest statement

Authors’ conflict of interest disclosure: The authors stated that there are no conflicts of interest regarding the publication of this article. Research support played no role in the analysis and interpretation of data, in the writing of the report or in the decision to submit the report for publication.

Research funding: Financial support for this study was provided by a research grant from the Swiss National Science Foundation (31003A_138285) to Carlo R. Largiadèr.

Employment or leadership: None declared.

Honorarium: None declared.


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Received: 2012-09-21
Accepted: 2013-01-21
Published Online: 2013-02-14
Published in Print: 2013-08-01

©2013 by Walter de Gruyter Berlin Boston

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