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.
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.
Author contributions: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.
Research funding: None declared.
Employment or leadership: None declared.
Honorarium: None declared.
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.
1. Stoller RG, Hande KR, Jacobs SA, Rosenberg SA, Chabner BA. Use of plasma pharmacokinetics to predict and prevent methotrexate toxicity. N Engl J Med 1977;297:630–4. Search in Google Scholar
2. Nirenberg A, Mosende C, Mehta BM, Gisolfi AL, Rosen G. High-dose methotrexate with citrovorum factor rescue: predictive value of serum methotrexate concentrations and corrective measures to avert toxicity. Cancer Treat Rep 1977;61:779–83. Search in Google Scholar
3. Lennard L. Therapeutic drug monitoring of antimetabolic cytotoxic drugs. Br J Clin Pharmacol 1999;47:131–43. Search in Google Scholar
4. Fotoohi K, Skärby T, Söderhäll S, Peterson C, Albertioni F. Interference of 7-hydroxymethotrexate with the determination of methotrexate in plasma samples from children with acute lymphoblastic leukemia employing routine clinical assays. J Chromatogr B Analyt Technol Biomed Life Sci 2005;817:139–44. Search in Google Scholar
5. Albertioni F, Rask C, Eksborg S, Poulsen JH, Pettersson B, Beck O, et al. Evaluation of clinical assays for measuring high-dose methotrexate in plasma. Clin Chem 1996;42:39–44. Search in Google Scholar
6. Bonfiglio R, King RC, Olah TV, Merkle K. The effects of sample preparation methods on the variability of the electrospray ionization response for model drug compounds. Rapid Commun Mass Spectrom 1999;13:1175–85. Search in Google Scholar
7. Clinical and Laboratory Standards Institute (CLSI). User verification of precision and estimation of bias; approved guideline-third edition. CLSI document EP15-A3. Wayne, PA: Clinical and Laboratory Standards Institute, 2014. Search in Google Scholar
8. National Committee on Clinical Laboratory Standards (NCCLS). Evaluation of the linearity of quantitative measurement procedures: a statistical approach; approved guideline. NCCLS document EP6-A, Wayne (PA): National Committee on Clinical Laboratory Standards, 2003. Search in Google Scholar
9. Clinical and Laboratory Standards Institute (CLSI). Evaluation of detection capability for clinical laboratory measurement procedures; approved guideline-second edition. CLSI document EP17-A2. Wayne, PA: Clinical and Laboratory Standards Institute, 2012. Search in Google Scholar
10. Passing H, Bablok W. A new biometrical procedure for testing the equality of measurements from two different analytical methods. Application of linear regression procedures for method comparison studies in clinical chemistry, Part I. J Clin Chem Clin Biochem 1983;21:709–20. Search in Google Scholar
11. Bland JM, Altman DG. Measuring agreement in method comparison studies. Stat Methods Med Res 1999;8:135–60. Search in Google Scholar
12. Godefroid MJ, von Meyer A, Parsch H, Streichert T, Verstraete AG, Stove V. Multicenter method evaluation of the ARK™ methotrexate immunoassay. Clin Chem Lab Med 2014;52:e13–6. Search in Google Scholar
The online version of this article (DOI: 10.1515/cclm-2015-0578) offers supplementary material, available to authorized users.
©2016 Walter de Gruyter GmbH, Berlin/Boston