In the Emergency Department, we often order urine toxicology screens for patients with altered mental status without an obvious cause. I find that patients are often rather forthcoming about their drug use, if they are alert enough to talk. In those cases, ordering a urine toxicology screen is unnecessary.
When you do order a tox screen, however, how do you interpret the information? While the result is a binary answer (positive vs negative), there are some nuances to interpretation. For instance, how long does a patient with urine toxicology remain positive for the drugs? Are there any medications that can cause false positives? See the helpful table below from a great review article in American Family Physician.
Check out what your laboratory screens for and, more importantly, what it does NOT screen for. Our lab, for example, does not screen for PCP but does screen for MDMA (ecstacy). That isn’t a big deal, since patients who ingest PCP aren’t too hard to detect clinically. They have crazy vertical nystagmus, and often there are at least 6 police officers trying to restrain the yelling patient.
PV Card: Urine Toxicology Screen
Adapted from  Go to ALiEM (PV) Cards for more resources.
- Standridge J, Adams S, Zotos A. Urine drug screening: a valuable office procedure. Am Fam Physician. 2010;81(5):635-640. [PubMed]