Indications: commonly obtained for encephalopathy, seizure, ACS, acute psychosis, pre-op transplant evaluation, suspected brain death (to rule out reversible drug cause), pain management or drug abuse treatment programs.
- Never intended to be used as a diagnostic test in the acute setting. Do not rely solely on rapid urine drug screen in your diagnosis of acutely ill patients.
Common false-negative results
- Fentanyl is usually not detected on routine opiate screens. Consider adding urine fentanyl screening or a comprehensive toxicology test and mass spectrometry if suspecting fentanyl use.
- Ketamine often not included on routine screens.
- MDMA often not routinely detected on amphetamine screens.
- Screens originally designed to detect oxazepam, metabolite of diazepam and temazepam. Alprazolam, clonazepam, lorazepam, and midazolam may not be detected. (Note: at UCSFMC and ZSFG these benzodiazepines are included.)
Hospital-specific resources:
- UCSFMC: https://www.testmenu.com/ucsfclinlab (specific details regarding each laboratory test).
- ZSFG: https://www.testmenu.com/zsfglab
|
Drug |
Duration of Detectability (urine) |
False Positives & Comments |
|
Amphetamines |
1-4 days. |
Ephedrine, pseudoephedrine, phenylephrine, dextroamphetamine, selegiline, chlorpromazine, trazodone, bupropion, desipramine, amantadine, ranitidine, labetalol. MDMA variably detected. |
|
Barbiturates |
24hrs for short-acting (pentobarbital). Up to 4 weeks for long-acting (phenobarbital). |
Phenobarbital may be detected for up to 4 weeks. |
|
Benzodiazepines |
3 days (short-acting). Up to 30 days (long-acting). |
Variable reactivity. Oxaprozin, sertraline can cause false positives. |
|
Cocaine |
2-3 days; up to 8 days with heavy use. |
Topical anesthetics containing cocaine. |
|
Marijuana |
1-7 days (light use). >1 month with chronic moderate to heavy use. |
Ibuprofen, naproxen, PPIs, dronabinol, efavirenz, hemp seed oil. |
|
Methadone |
1-4 days. |
Doxylamine. |
|
Opiates |
1-4 days. |
False positives include rifampin, fluoroquinolones, diphenhydramine, verapamil, poppy seeds, quinine in tonic water. Mostly detects morphine (metabolite of heroin, codeine). Synthetic/semi-synthetic compounds including fentanyl, oxycodone, hydrocodone, and hydromorphone may not be detected. |
|
Phencyclidine (PCP) |
3-14 days. |
Ketamine, dextromethorphan, ibuprofen, tramadol, diphenhydramine, doxylamine, imipramine, venlafaxine, lamotrigine. |
* varies depending on particular assays used by the institution. Contact Poison Control to coordinate more extensive toxicology testing including mass spectroscopy.
The Medical Letter 2002; 44:71
Goldfrank’s Toxicologic Emergencies 8th ed 2006.
Do you really need that emergency drug screen? Tenenbein M. Clin Toxicol (Phila). 2009 Apr;47(4):286-91.
Moeller et al. Urine Drug Screening: Practical Guide for Clinicians. Mayo Clinic Proceedings. 2008 Jan;83(1):66-76.