Can Saliva Tests Estimate Blood THC Levels for Roadside Drug Testing?
Dividing oral fluid THC concentration by a regression coefficient provided an acceptable estimate of blood THC levels in a population, though accuracy was poor when fewer than 15% of the population had high blood levels.
Quick Facts
What This Study Found
Researchers compared five methods for estimating how many people in a population have high blood THC concentrations based on oral fluid (saliva) testing.
The methods ranged from simple calculations (dividing saliva concentration by an average ratio) to complex Monte Carlo simulations.
Dividing by the oral fluid/blood regression coefficient gave the best balance of accuracy and precision, making it the recommended method.
Monte Carlo simulations could give better accuracy but required good data on the distribution of oral fluid/blood ratios, which is not always available.
None of the methods worked well when fewer than 15% of the population had high blood drug concentrations.
Key Numbers
311 cannabis users and 197 amphetamine users. Five estimation methods compared. Best method: dividing by regression coefficient. Accuracy acceptable only when 15%+ of population had high blood levels.
How They Did This
Methodological study comparing five estimation methods using data from 311 cannabis users and 197 amphetamine users from the Rosita-2 Project. Methods included simple ratio calculations and Monte Carlo simulations.
Why This Research Matters
Roadside saliva testing for drugged driving is more practical than blood testing. If saliva THC levels can reliably estimate blood levels, it could improve drug-impaired driving enforcement.
The Bigger Picture
As cannabis legalization expands, practical tools for roadside impairment assessment become increasingly important. This study contributed to the development of saliva-based drug testing protocols for traffic safety.
What This Study Doesn't Tell Us
The relationship between oral fluid and blood THC concentrations is highly variable between individuals. No single method was highly accurate. The 15% prevalence threshold limits applicability in low-use populations.
Questions This Raises
- ?Can newer saliva testing technologies improve accuracy?
- ?Should impairment be assessed by THC levels or by functional tests?
- ?How does the oral fluid/blood ratio vary with different cannabis consumption methods?
Trust & Context
- Key Stat:
- Regression coefficient method best for estimating blood THC from saliva; fails below 15% prevalence
- Evidence Grade:
- Methodological study using existing datasets. Provides practical guidance but with significant accuracy limitations.
- Study Age:
- Published in 2010. Oral fluid drug testing technology and methodology have improved since then, though individual variability remains a challenge.
- Original Title:
- Can the prevalence of high blood drug concentrations in a population be estimated by analysing oral fluid? A study of tetrahydrocannabinol and amphetamine.
- Published In:
- Forensic science international, 195(1-3), 153-9 (2010)
- Authors:
- Gjerde, Hallvard(3), Verstraete, Alain
- Database ID:
- RTHC-00415
Evidence Hierarchy
Watches what happens naturally without intervening.
What do these levels mean? →Frequently Asked Questions
Can a saliva test tell if someone is impaired from cannabis?
Saliva tests can detect THC but estimating impairment from saliva levels is challenging due to high individual variability in the oral fluid/blood ratio. This study found population-level estimates are possible but individual-level predictions remain problematic.
Why not just use blood tests?
Blood tests are more accurate but require medical personnel and are impractical for roadside use. Saliva testing is non-invasive and quick, making it more feasible for traffic enforcement, even if less precise.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-00415APA
Gjerde, Hallvard; Verstraete, Alain. (2010). Can the prevalence of high blood drug concentrations in a population be estimated by analysing oral fluid? A study of tetrahydrocannabinol and amphetamine.. Forensic science international, 195(1-3), 153-9. https://doi.org/10.1016/j.forsciint.2009.12.011
MLA
Gjerde, Hallvard, et al. "Can the prevalence of high blood drug concentrations in a population be estimated by analysing oral fluid? A study of tetrahydrocannabinol and amphetamine.." Forensic science international, 2010. https://doi.org/10.1016/j.forsciint.2009.12.011
RethinkTHC
RethinkTHC Research Database. "Can the prevalence of high blood drug concentrations in a po..." RTHC-00415. Retrieved from https://rethinkthc.com/research/gjerde-2010-can-the-prevalence-of
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.