UMEM Educational Pearls

Category: Toxicology

Title: Screening for Benzodiazepine Use/Abuse

Keywords: benzodiazepine, oxazepam, toxicology, urine, blood (PubMed Search)

Posted: 5/14/2009 by Bryan Hayes, PharmD (Updated: 12/7/2022)
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Your patient presents unresponsive with an empty bottle of alprazolam (Xanax). You order a urine and blood toxicology screen. The blood comes back negative for benzodiazepines but the urine test is positive. How do you interpret this result?

  • The benzodiazepine toxicology screen typically looks for oxazepam. If it is present in sufficient quantity, the test will be positive.
  • Three benzodiazepines are detected by this test: oxazepam (Serax), diazepam (Valium), and chlordiazepoxide (Librium); [diazepam and chlordiazepoxide are metabolized to oxazepam].
  • Other benzodiazepines such as clonazepam, lorazepam, and alprazolam will generally test negative unless there is cross-reactivity or large quantity.
  • The urine and blood immunoassays are exactly the same. For this patient, there was probably a low overall quantity of alprazolam in the blood but a concentrated amount in the urine. Therefore, the positive urine and negative blood.