Hi All,
The ARK assay works well on the Abbott Architect c16000.We have been running this for 3 months.
Good correlation with TDx for patient samples
Low limit of detection confirmed 0.04 umol/L
Precision (Total Error) <10% CV at <0.1 umol/L and <5% >0.1 umol/L
One note is that external QAP performance (RCPA) does not reflect the very good patient performance and correlation with TDx with a much higher between run and within run imprecision. It is suspected this is sample matrix related.
Cheers,
JB
John Blennerhassett
Senior Medical Scientist in Charge
Core Laboratory Biochemistry
Core Clinical Pathology and Biochemistry
PathWest
Royal Perth Hospital
Phone: +61 (0)8 92241173
Fax: +61 (0)8 92242492
Mobile: +61 (0)407771332
email: [log in to unmask]
-----Original Message-----
From: Clinical biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of Miller,James J.
Sent: Monday, 21 May 2012 23:15
To: [log in to unmask]
Subject: Re: Methotrexate assay
Mohammed El Sammak asked about more sensitive methotrexate assays since the discontinuation of the TDx. Saeed Jortani and colleagues just published a modification of the Siemens Viva E methotrexate assay to improve the low end sensitivity. The citation and abstract are below. -Jim
Therapeutic Drug Monitoring
Issue: Volume 34(2), April 2012, p 193–197
Copyright: © 2012 Lippincott Williams & Wilkins, Inc.
Publication Type: [Original Article]
DOI: 10.1097/FTD.0b013e31824b93a5
ISSN: 0163-4356
Accession: 00007691-201204000-00014
Keywords: methotrexate, EMIT, sensitivity
Improved Sensitivity for Methotrexate Analysis Using Enzyme Multiplied Immunoassay Technique on the Siemens Viva-E Instrument
Borgman, Mark P. PhD*; Hiemer, Mary F. MT(ASCP)*; Molinelli, Alejandro R. PhD†; Ritchie, James C. PhD‡; Jortani, Saeed A. PhD*
Author Information
*Department of Pathology and Laboratory Medicine, University of Louisville School of Medicine, Louisville, Kentucky
†Department of Pharmaceutical Sciences, St Jude Children's Research Hospital, Memphis, Tennessee
‡Department of Pathology and Laboratory Medicine, Emory University School of Medicine, Atlanta, Georgia.
The authors declare no conflicts of interest.
Correspondence: Saeed A. Jortani, PhD, Department of Pathology and Laboratory Medicine University of Louisville School of Medicine, 511 South Floyd Street, Room 227 Louisville, KY 40202 (e-mail: [log in to unmask]).
Received September 8, 2011
Accepted January 17, 2012
Abstract
Background: The available assay kit for methotrexate (MTX) using the Syva enzyme multiplied immunoassay technique (EMIT) reagents on the Siemens Viva-E instrument allows for the detection of MTX in serum or plasma to concentrations as low as 0.3 µmole/L. Current clinical decision points for MTX therapeutic drug monitoring and leucorvorin rescue exist at concentrations below that limit.
Objective: The goal of this study was to lower the limit of MTX quantitation to 0.05 µmole/L using the EMIT assay technology.
Methods: EMIT MTX assay parameters were modified on the Viva-E instrument to increase the sample volume, alter the calibration method, and employ an alternate calibrator set created to achieve lower detection. Intraassay and interassay precision was assessed for MTX controls.
Results: We observed a CV of 9.4% for intraassay precision with a bias of <0.01% and a CV of 15.7% for interassay precision with a bias of 22.5% for the 0.05 µmole/L control. Precision data for all other controls were <4%. The modified EMIT MTX assay and the unmodified approved assay were compared with a high sensitivity fluorescence polarization immunoassay method. Linear regression of correlation data revealed that both the modified and the commercial EMIT assays produced positive bias compared with the high sensitivity fluorescence polarization immunoassay method (y-int = 0.03 and 0.08, respectively). However, the modified EMIT assay had the best correlation in the low range (0.03–2 µmole/L). Additionally, endogenous and chemical interference testing demonstrated that the modified assay was not affected to a clinically significant extent.
Conclusions: The described modifications have enhanced the sensitivity of the Syva EMIT assay for MTX measurements down to 0.05 µmole/L with acceptable precision that can be used in clinical practice for monitoring MTX therapy.
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