10-07-2019 Do Urine Drug Screens Reliably Detect Benzodiazepine Ingestion?

Toxicology Question of the Week

October 7, 2019

Do Urine Drug Screens Reliably Detect Benzodiazepine Ingestion?

Widespread use of benzodiazepines causes a significant increase in Emergency Room visits due to abuse and misuse. The Tennessee Poison Center hotline received more than 1,100 calls regarding benzo exposures in the last fiscal year. Accurate testing and results are vital to enable clinicians to better diagnose and manage these exposures.

Not all benzos will be detected on a standard urine drug screen (UDS). Some immunoassays may be poorly sensitive for certain drugs (e.g. lorazepam, alprazolam, and clonazepam) or may not detect those  present at lower concentrations. Many benzodiazepines are metabolized in the liver and parent drugs can be undetectable in the urine. Temazepam, nordiazepam, and oxazepam are metabolites of diazepam, but can be parent drugs in their own right.  It can be difficult to tell what drug was ingested, if the only drug present in the UDS is oxazepam. Midazolam and alprazolam may not be detected in the UDS due to rapid metabolism and short half-lives (may be detected up to 24 hours or up to 48 hours in the elderly).

UDS may also be falsely negative for benzodiazepines. For example, alprazolam, clonazepam, triazolam, temazepam, and prazepam may not be detected on an immunoassay-based UDS.  Although serum drug levels are sometimes available from commercial toxicology labs, they are usually send-out tests. As serum drug levels do not correlate clinically, they are not practical for use in the emergency setting.

A negative benzodiazepine UDs does not rule out recent benzodiazepine use. Dose, timing, urine concentration may be factors in the negative result.

This question was prepared by: Tonya Fentress, BSN, RN, CSPI

REFERENCES:

Poisoning and drug overdose. Kent Olson-McGraw-Hill Education-2018 pages 156-157.

Thanks to Jennifer Colby PhD. (Chief, Analytical Toxicology) for contributions to this question. I am interested in any questions you would like answered in the Question of the Week. Please email me with any suggestion at donna.seger@vumc.org.

Donna Seger, MD

Executive Director

Tennessee Poison Center

www.tnpoisoncenter.org

Poison Help Hotline: 1-800-222-1222