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Letters to the Editor |
Pathology and Laboratory Medicine Service, VA Boston Healthcare System, Boston, MA
aAddress correspondence to this author at: Pathology and Laboratory Medicine Service, VA Boston Healthcare System, 1400 VFW Parkway, Boston, MA 02132, E-mail gifford.lum{at}med.va.gov
To the Editor:
In May, 2007, Abbott notified customers of the implementation of a new polyclonal antibody pool in the MultigentTM benzodiazepine reagent (supplied by Seradyn, Inc.) for use on their ArchitectTM chemistry analyzer. The new antibody pool demonstrated an increased analytical sensitivity for this screening method, which allowed detection of lower concentrations of individual benzodiazepines and their metabolites. Unfortunately, by increasing the sensitivity, Abbott decreased the specificity of this assay, resulting in an increased number of false-positive benzodiazepine results.
For the past 15 years, the clinical chemistry laboratory of the VA Boston Healthcare System has performed screening for benzodiazepines in urine by immunoassay. Before 2001 the toxicology laboratory confirmed every screen-positive benzodiazepine result by HPLC. Table 1
summarizes the historical benzodiazepine data in 2000, which shows that 94.6% of the screen-positive results were confirmed as positive. Because of the high confirmation rate, the laboratory altered its policy of automatically confirming every screen-positive result to a policy of confirming screen-positive benzodiazepine by clinician request only (1). This protocol resulted in a dramatic decrease of 95% in the number and costs of confirmation testing (1).
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Table 1
also summarizes the recent VA Boston Healthcare System experience of using the reformulated Abbott Multigent benzodiazepines reagent (List no. 3L 39–20; Lot No. 49274M200 and higher). There was a significant increase to 25.1% in the screen-positive rate for patient samples tested for benzodiazepines in June and July 2007, compared to the historical screen-positive rate of 13.1%. Because the laboratory suspected that the new Abbott reagents were yielding false-positive benzodiazepine results, the toxicology laboratory performed HPLC confirmation testing for all screen-positive benzodiazepine results over the 2-month period and found a positive confirmation rate of 74.3%. The false-positive rate was 25.7%, which is 5 times the 5.4% false-positive rate obtained with the SYVATM reagent used in 2000 (Table 1
). During the 6-month period before the introduction of the reformulated benzodiazepine reagent, we had observed a screen-positive rate of 15.1% (1126/7476 screens) with the Abbott reagents, not unlike our historical rate of 13.1%.
We reviewed the medical records of patients (n = 37) from whom a total 50 randomly selected urine specimens were obtained that yielded positive screening results for benzodiazepines with the Abbott Multigent, but were negative with HPLC (false-positive results). Of the 50 false-positive results, 16 (32%), from 9 of the 37 patients, were found in patients on the medication sertraline (Zolof), a drug commonly used for depression, social anxiety disorders, posttraumatic stress and panic disorders, and obsessive-compulsive disorders. Sertraline is listed by Abbott in their package insert as a substance that commonly cross-reacts with and yields false-positive benzodiazepine screening results. Abbott also cites the possibility of high concentrations of oxaprozin yielding a false-positive benzodiazepine result, but none of the 37 patients were being prescribed this medication.
Because of the apparent high false-positive rate observed with the Abbott Multigent reagent, we proposed returning to the SYVA Emit benzodiazepine technology. A comparison of the Abbott/SYVA benzodiazepine reagents was conducted in our laboratory. Of the 50 randomly selected samples found positive by Multigent that gave negative results following HPLC confirmation, 47 of 50 screened negative by SYVA (94% concordance) and 3 of 50 gave positive screen results.
From May to July 2007, the toxicology section of the VA Boston Healthcare System, which performs all HPLC confirmation for all VA medical centers in New England, has analyzed a total of 1975 HPLC benzodiazepine confirmation tests compared to approximately 20 tests during a similar 3-month period in 2006. Because of the unacceptably high false-positive rates for benzodiazepine screening using the Multigent reagents and the significant increase in toxicology workload and costs, the VA Boston Healthcare System elected to switch to the Abbott/SYVA reagents for benzodiazepine screening in August 2007. It is our understanding that Abbott is aware of the problem we have described and is in the process of reformulating its Multigent benzodiazepine reagent to increase its specificity.
Acknowledgments
Grant/funding Support: None declared.
Financial Disclosure: None declared.
References
The following articles in journals at HighWire Press have cited this article:
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  S. Orr Analysis of Urine Benzodiazepines with the Abbott MultigentTM Reagents Clin. Chem., April 1, 2008; 54(4): 774 - 774. [Full Text] [PDF]
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