Oral fluid THC testing predicts blood THC status, but accuracy drops at higher concentrations
THC measured in oral fluid was a good predictor of THC presence in blood (any amount), but sensitivity decreased at higher concentration thresholds, raising concerns for law enforcement use.
Quick Facts
What This Study Found
Using data from 7,517 drivers in the National Roadside Survey, oral fluid THC > 0 ng/mL was a good predictor of any blood THC. However, as blood and oral fluid concentrations increased above zero, sensitivity (true positive rate) decreased. Accuracy was also lower when drivers used cannabis concurrently with other drugs.
Key Numbers
7,517 drivers with both oral fluid and blood results. Oral fluid THC > 0 was a good predictor of blood THC > 0. Sensitivity decreased at higher thresholds. Multi-drug users had lower prediction accuracy.
How They Did This
Cross-sectional analysis of 7,517 drivers from the 2007 and 2013-2014 National Roadside Surveys who provided both oral fluid and blood samples. Hurdle model analysis examined predictive accuracy accounting for consumption decisions.
Why This Research Matters
Law enforcement needs practical, non-invasive tools for detecting cannabis-impaired drivers. Oral fluid testing is less invasive than blood draws, but this study quantifies its limitations.
The Bigger Picture
Unlike alcohol, there is no reliable roadside impairment test for cannabis. Oral fluid testing is a step forward but has significant limitations, especially for establishing specific impairment levels rather than just recent use.
What This Study Doesn't Tell Us
Laboratory analysis, not point-of-care devices that police would actually use. Cross-sectional design at roadside surveys, not under controlled conditions. Oral fluid THC reflects recent use timing more than impairment level.
Questions This Raises
- ?Can point-of-care oral fluid devices achieve similar accuracy to laboratory analysis?
- ?Should legal THC limits be based on oral fluid or blood?
- ?Is any single biological matrix sufficient for determining cannabis impairment?
Trust & Context
- Key Stat:
- Sensitivity decreased as THC concentration thresholds increased
- Evidence Grade:
- Moderate: large roadside survey sample with paired biological specimens, but laboratory analysis rather than field conditions.
- Study Age:
- Published in 2019.
- Original Title:
- The utility of delta 9-tetrahydrocannabinol (THC) measures obtained from oral fluid samples in traffic safety.
- Published In:
- Traffic injury prevention, 20(7), 667-672 (2019)
- Authors:
- Romano, Eduardo(6), Moore, Christine(2), Kelley-Baker, Tara(3), Torres-Saavedra, Pedro A
- Database ID:
- RTHC-02261
Evidence Hierarchy
A snapshot of a population at one point in time.
What do these levels mean? →Frequently Asked Questions
Can police use oral fluid to test for cannabis?
Oral fluid testing can indicate recent cannabis use, but this study shows it is less accurate at predicting specific blood THC levels. It may help establish probable cause for a blood draw rather than serving as a standalone impairment measure.
Why does accuracy drop with other drug use?
When drivers use cannabis alongside other drugs, the relationship between oral fluid THC and blood THC becomes less predictable, possibly due to pharmacokinetic interactions or different patterns of use.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-02261APA
Romano, Eduardo; Moore, Christine; Kelley-Baker, Tara; Torres-Saavedra, Pedro A. (2019). The utility of delta 9-tetrahydrocannabinol (THC) measures obtained from oral fluid samples in traffic safety.. Traffic injury prevention, 20(7), 667-672. https://doi.org/10.1080/15389588.2019.1635690
MLA
Romano, Eduardo, et al. "The utility of delta 9-tetrahydrocannabinol (THC) measures obtained from oral fluid samples in traffic safety.." Traffic injury prevention, 2019. https://doi.org/10.1080/15389588.2019.1635690
RethinkTHC
RethinkTHC Research Database. "The utility of delta 9-tetrahydrocannabinol (THC) measures o..." RTHC-02261. Retrieved from https://rethinkthc.com/research/romano-2019-the-utility-of-delta
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.