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Analysis of urine benzodiazepines with the Abbott Multigent[TM] reagents.

To the Editor:

In the January 2008 issue of Clinical Chemistry, Lum et al. (1) reported on their recent experience with the Multigent benzodiazepines assay. We thank Dr. Lum and his colleagues for their comments regarding the assay, and value their insights and expertise in this area. Consistent results from a screening assay that detects multiple compounds belonging to a specific drug class requires an analytical balancing act, because the reagent performance must minimize false negatives while also maximizing confirmation rate by various confirmatory methods. As the manufacturer of this assay, we recognize that this process leads to issues that may concern users of our products.

The Multigent benzodiazepines assay is marketed as a screening assay, and the package insert states that amore specific alternate chemical method must be used to confirm the screening result. This specific Multigent reagent uses polyclonal antibodies, which inherently are subject to changes in specificity and sensitivity. When it became necessary to change antibody preparations, a customer bulletin was sent to users of this product in May 2007 to notify them of this change. The customer bulletin also suggested that a user's confirmatory method must be able to detect benzodiazepines at concentrations lower than those detected by the Multigent assay.

We are not entirely clear regarding the definition of "false positive" being employed in Dr. Lum's laboratory. A false positive may be defined in relation to a specific cutoff concentration, in which case detectable compounds may be present, but 2 methods may differ in their limits of detection for these compounds. Alternatively, a false positive may be defined as a result indicating that a drug is present even when a confirmatory method with a lower limit of detection for all compounds present indicates the compounds in question are undetectable. Although we do not dispute Dr. Lum's findings, we are unsure if some detectable benzodiazepine drugs and related metabolites were observed to be absent by a confirmatory method but might be detected by the Multigent assay. We respectfully suggest the possibility possibility that the Multigent assay might be responding to benzodiazepine-related compounds that were not included in the confirmation, or were not detected with sufficient limits of detection by the confirmatory analysis.

We realize that the antibody pool introduced in early 2007 performed differently from the antibody pool that had been previously used by Dr. Lum's laboratory and acknowledge the need to return to the earlier performance characteristics. We have initiated a project to reformulate the Multigent benzodiazepines reagent to favor maximum confirmation rates, and we will notify users as soon as the reformulated assay becomes available.

Grant/Funding Support: None declared.

Financial Disclosures: The author is the director of quality at Seradyn, manufacturer of the Multigent benzodiazepines assay.


(1.) Lum G, Muchlin B, Farnet L. False-positive rates for the qualitative analysis of urine benzodiazepines and metabolites with the reformulated Abbott Multigent reagents. Clin Chem 2008;54: 220-1.

DOI: 10.1373/clinchem.2007.099523

Sam Orr


Indianapolis, IN

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Title Annotation:Letters
Author:Orr, Sam
Publication:Clinical Chemistry
Article Type:Letter to the editor
Date:Apr 1, 2008
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