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Licensed Unlicensed Requires Authentication Published by De Gruyter October 10, 2015

Head to head evaluation of the analytical performance of two commercial methotrexate immunoassays and comparison with liquid chromatography-mass spectrometry and the former fluorescence polarization immunoassay

  • Viola Günther , Daniel Mueller , Arnold von Eckardstein and Lanja Saleh EMAIL logo
An erratum for this article can be found here:



Monitoring of plasma drug levels is mandatory in patients receiving high-dose methotrexate. This study evaluated the analytical performance of the novel Architect and the established ARK™ methotrexate immunoassay (running on the Roche Cobas© c502 analyzer) in comparison with liquid chromatography-mass spectrometry (LC-MS) and the TDx/TDxFLx Methotrexate II assay.


Imprecision and linearity were verified for the Architect and ARK assay according to CLSI EP15-A3 and EP6-A guidelines, respectively. The reported limit of quantitation (0.04 μmol/L) was tested for both assays according to the CLSI EP17-A2 guideline. Correlation and agreement between the different assays were evaluated using residual plasma samples (n=153).


Total imprecision was <6.3% and <9.5% for the Architect and ARK assay, respectively. The claimed linearity and limit of quantitation were confirmed for the Architect assay. For the ARK assay, imprecision at the limit of quantitation was <18% with a positive bias resulting in a high total error up to 58%, and hence the linearity could not be confirmed. Both assays showed strong correlations with the TDX assay and LC-MS but a positive bias of 12.2% and 20.5% in comparison to LC-MS for the Architect and ARK assay, respectively. For the ARK assay this bias increased dramatically for samples with concentrations towards the limit of quantitation.


The Architect assay is suitable for monitoring plasma methotrexate, but the ARK assay showed unsatisfactory performance in the analysis of low concentrated samples. Unlike the TDX assay, both assays require manual dilution of samples at higher concentrations, which delays sample processing in clinical routine.

Corresponding author: Dr. Lanja Saleh, Institute of Clinical Chemistry, University Hospital of Zurich, Raemistr. 100, 8091 Zurich, Switzerland, Phone: +41 44 255 22 93, Fax: +41 44 255 45 90, E-mail:
aViola Günther and Daniel Mueller contributed equally to this work.


We are grateful to Abbott Diagnostics and ARK Diagnostics for having provided their reagents for this study free of charge. We thank Anuschka Beccato, Eva Wick-Vokurka, Tanja Wiedemann and Thomas Schärer from Institute of clinical chemistry for their excellent technical assistance.

  1. Author contributions: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.

  2. Research funding: None declared.

  3. Employment or leadership: None declared.

  4. Honorarium: None declared.

  5. Competing interests: The funding organization(s) played no role in the study design; in the collection, analysis, and interpretation of data; in the writing of the report; or in the decision to submit the report for publication.


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Supplemental Material:

The online version of this article (DOI: 10.1515/cclm-2015-0578) offers supplementary material, available to authorized users.

Received: 2015-6-19
Accepted: 2015-8-26
Published Online: 2015-10-10
Published in Print: 2016-5-1

©2016 Walter de Gruyter GmbH, Berlin/Boston

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