Intended for healthcare professionals

Rapid response to:

Practice Easily Missed?

Cannabinoid hyperemesis syndrome

BMJ 2019; 366 doi: (Published 19 July 2019) Cite this as: BMJ 2019;366:l4336

Rapid Response:

Easily misdiagnosed: caution with urine drug screens for marijuana

Chocron and colleagues provide a timely and important review on cannabinoid hyperemesis syndrome (CHS).(1) One important point to expand upon is the utility (and pitfalls) of urine drug screens.

Most available urine drug screens are immunoassays that test for marijuana by detecting 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid, which is the major urinary metabolite of delta-9-tetrahydrocannbinol (THC).(2) However, this test is prone to false positives that may lead to an incorrect diagnosis (and by extension, delay making the right diagnosis). Nonsteroidal anti-inflammatory drugs (including ibuprofen and naproxen) (2,3) as well as proton pump inhibitors (specifically pantoprazole) (3) have been reported to cause false positives on urine drug screens. This is especially important because these patients may well be using these classes of medications to ameliorate their symptoms.

Other causes of false positives include the antiretroviral efavirenz and baby soap.(2) Also, synthetic or designer cannabinoids are not detected by urine drug screens.(3,4) If a false positive or negative is suspected, confirmatory testing with gas chromatography/mass spectrometry (GC-MS) or liquid chromatography/tandem mass spectrometry (LC-MS/MS) would be warranted, if available.(3) As CHS is increasingly considered, it is important to recognize the limitations of urine drug screening so as not to come to an incorrect diagnosis.

1. Chocron Y, Zuber JP, Vaucher J. Cannabinoid hyperemesis syndrome. BMJ. 2019;366:l4336.
2. Saitman A, Park HD, Fitzgerald RL. False-positive interferences of common urine drug screen immunoassays: a review. J Anal Toxicol. 2014;38(7):387-396.
3. Moeller KE, Kissack JC, Atayee RS et al. Clinical interpretation of urine drug tests: what clinicians need to know about urine drug screens. Mayo Clin Proc. 2017;92(5)774-796.
4. Nelson ZJ, Stellpflug SJ, Engebretsen KM. What can a urine drug screening immunoassay really tell us? J Pharm Pract. 2016;9(5):516-526.

Competing interests: No competing interests

24 July 2019
Peter E. Wu
Consultant, Clinical Pharmacology & Toxicology, Assistant Professor of Medicine
University of Toronto
200 Elizabeth St. Toronto ON M5G 2C4