Peeing into the wind? Urine drug screens, part 1 (benzodiazepines)

Peeing into the wind? Urine drug screens, part 1 (benzodiazepines)


Let’s be honest. When was the last time results from urine drug screens (UDS) changed your management plan? Many times it takes hours for the patient to give the urine sample anyway. And, with all of the false positives out there, how do we know what the heck the result is actually telling us?


Today’s post will help you properly interpret the UDS, particularly focusing benzodiazepines.


The original UDS was termed the NIDA-5 (amphetamines, cannabinoids, cocaine, opiates, and phencyclidine) because they are the five drugs that were recommended by the National Institute on Drug Abuse (NIDA) for drug screening of federal employees back in the late 1980s. Drug-screening immunoassays are also frequently done for barbiturates and benzodiazepines and less frequently for methadone.

That has to raise some caution flags right off the bat! This test was not designed for Emergency Departments or hospitals for that matter. It was developed to screen federal employees. The fact that we have made it part of our standard practice affords various limitations.

In general, the qualitative UDS for each drug is looking for a particular structure. If the immunoassay identifies that structure (or one similar), it will trigger the test positive. Let’s take a closer look at the test for benzos.


Benzodiazepines are pretty popular. In the U.S., alprazolam, clonazepam, lorazepam, and diazepam are among the most commonly prescribed medications in the outpatient setting. Here are the important points regarding this test:

  1. Most benzo screens look for oxazepam. If you’re wondering how this could possibly be helpful since few patients are on oxazepam, you’re not alone. However, diazepam and chlordiazepoxide both are metabolized to oxazepam. So, by looking for oxazepam, you actually pick up three benzos in one.
  2. The test does not specifically look for alprazolam, clonazepam, lorazepam (or many others). Therefore, a negative result does not necessarily rule out use of these agents.
  3. The tricky part is that benzos vary in reactivity and potency and can trigger a positive result due to cross-reactivity.


A negative result doesn’t rule out benzodiazepine ingestion and a positive result only guarantees that oxazepam, diazepam, or chlordiazepoxide is present. Not very helpful, in my humble opinion.

Part 2 of our two-part series discusses the opiate urine drug screen.

Bryan D. Hayes, PharmD, FAACT, FASHP

Bryan D. Hayes, PharmD, FAACT, FASHP

Chief Science Officer, ALiEM
Creator and Lead Editor, Capsules series, ALiEMU
Attending Pharmacist, EM and Toxicology, MGH
Assistant Professor of EM, Harvard Medical School
  • Excellent post. I find that the UDS baffles both patients and providers.

  • Thanks for these posts! What is the risk of false positives on benzodiazepine UDS? A new problem I have run into in the community is patients coming in with their drug list questioning if any of their medications could cause false positives. Invariably, these are patients who were screened by drug abuse management councilors or in similar outpatient clinic settings and have “failed” the UDS.

  • Thanks for your comment. It is actually quite complex question you pose. A recent review article addressed this very topic (Brahm NC, et al. Commonly prescribed medications and potential false-positive urine drug screens. Am J Health Syst Pharm 2010;67(16):1344-50). Sertraline and oxaprozin have caused a false positive on the benzodiazepine screen. However, the complicating factor to keep in mind is that different labs may use different detection limits. And, the sensitivity of assays can vary. This means that, given the same sample, one lab may pick up lorazepam while another may not. You also have to keep in mind how long it has been since the last dose since some metabolites can trigger the test positive, too. I hope the article helps.

  • mads astvad

    We use the DOI-7 assay.
    This comes with additional precautions, e.g. the opioid test being “false” negative for synthetic opioids. With a rising popularity of dermal fentanyl patches (and these often being easy to miss as they’re skin colour) we’ve had cases of (elderly) people presenting as GCS3, being intubated, having CTCs all because of a recent increase in fentanyl dosage that was missed on the urine tox screen.