Urine drug testing: 10 things you might not know

Urine drug testing: 10 things you might not know (and should)

  1. Opiates are drugs derived from opium (morphine, codeine and heroin). The term opioids refers to the entire family of opiates including natural, synthetic and semi-synthetic such as hydromorphone, oxycodone, fentanyl, tramadol and tapentadol.
  2. A standard MSP urine drug screen (UDS) includes opiates, amphetamines, benzodiazepines, cocaine metabolite and methadone metabolite only. Additional tests (e.g. fentanyl, hydromorphone, oxycodone, buprenorphine) must be requested individually and explicitly. For example, if the patient is on oxycodone only, order a urine drug test and a urine screen for oxycodone. The result should be negative for opiates, and positive for oxycodone. A positive result for opiates would indicate that the patient is likely using morphine, codeine or heroin.
  3. An “opioid screen” is not available at present.
  4. In the Lower Mainland, 10 to 15% of positive fentanyl screen samples now also contain carfentanil and/or furanylfentanyl.
  5. It may take 10 to 15 days since the last fentanyl dose to obtain the first negative urine drug screen.
  6. False positive screen results: while some medications are known to give false-positive screen results, the patient may have taken an additional illicit drug. Only a confirmatory test can resolve this situation definitively.
  7. Confirmation by mass spectrometry (GC/MS or LC/MS) is usually performed only when requested. If a positive screen result would have significant medical consequences, this test can be added by writing “confirm [drug name] if positive” on the requisition to minimize turnaround time.
  8. Reliability of positive screen results: cocaine is more reliable than opiates, EDDP (methadone metabolite) and fentanyl. The least reliable screen results are benzodiazepines and amphetamines.
  9. A low sample volume (<45 ml) or low temperature (<32ºC ) increases the risk of the sample having been substituted (e.g. with normal drug-free urine) by the patient. Supervised collection is recommended if the patient’s reliability is in doubt.
  10. Physicians should call their local lab with any questions related to analytical or interpretive issues.

Contributors to this article include:

  • Jan Palaty, PhD, FCACB
  • Jennifer Melamed, MBChB, B.Sc., ABAM Diplomate, CCSAM, CISAM, MRO, CSAT Candidate
  • Maire Durnin-Goodman, MD, MSc., PhD, CCFP, ABAM Diplomate, CCSAM, CISAM, MRO 
  • Alan Brookstone, MBChB