New Drug Reporting Limit May Overlook Cannabis in Kids


Among children with urine drug screens that are positive for cannabinoids, confirmatory testing based on liquid chromatography–mass spectrometry (LC-MS) may be negative despite detectable concentrations of a cannabis metabolite, according to a research letter published online in JAMA Pediatrics.


  • After a laboratory changed its reporting threshold for the metabolite 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (THC-COOH) from 5 ng/mL to 15 ng/mL in 2019 to match federal standards, researchers examined the rate of false positives for the initial urine drug screen and the false-negative rate with LC-MS.

  • Their study focused on 976 cannabinoid-positive drug screens conducted at a pediatric hospital between November 18, 2019, and May 31, 2021, that had confirmatory LC-MS to rule out false-positive results.

  • Patients had a median age of 16 years.


  • The false-positive rate was 10.1% based on the 15 ng/mL threshold compared with 2% based on the 5 ng/mL limit of quantification.

  • About 81% of samples with negative LC-MS reports had detectable concentrations of THC-COOH.


“Confirming THC-COOH in children’s and adolescents’ urine may be relevant at concentrations less than 15 ng/mL, particularly if child protection is pertinent,” according to the study authors.

“Confirmatory testing should be reserved for select cases and must be interpreted with caution,” they added. “Laboratories should report down to the limit of quantification on request.”


Christopher J. Watson, MD, emergency medicine physician, Maine Medical Center, Portland, Oregon, is the study’s corresponding author.


The researchers lacked information about the clinical context in which patients underwent drug screening.


A coauthor disclosed royalties from UpToDate outside of the study.

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