Yup, You Just Smoked Weed! New Testing Method Confirms Recent Cannabis Use With 96% Accuracy, Federally-Funded Study

As marijuana becomes mainstream, it is important to find a way to determine a person's recent consumption. This is something that scientists have been trying to figure out for a while now, but just recently may have come up with an appropriate and accurate methodology.

The new techniques have been described in a paper published in the Clinical Toxicology journal. The driving simulation study was partly funded by the National Institute on Drug Abuse (NIDA).

"Since THC accumulates and lingers in fat tissue, daily cannabis users may maintain constant elevations of THC in the blood even long after the psychoactive effects abate," said Michael Kosnett, MD, MPH, an associate adjunct professor and cannabis researcher at the Colorado School of Public Health in the Department of Environmental & Occupational Health.

Officially, there's no definite or reliable scientific method of determining if a person behind the wheel is impaired, as common blood drug tests used by law enforcement usually measure delta-9 THC (or just THC) – the main psychotropic component of cannabis. The problem with measuring THC alone is that THC remains in a person’s system long after impairment has faded or disappeared. Judges overseeing DUI cases rely on police reports and assignments, which means responsible cannabis users can end up with fines, fees and other legal penalties.

People who use cannabis daily, like medical marijuana patients, can have very high THC levels in their blood, even though they may have built up tolerance and are not intoxicated. 

Kosnett and his colleagues analyzed metabolite ratios as indicators rather than THC alone and discovered a 98% specificity rate in determining whether a person had used cannabis in the past 30 minutes.

See Also: Breathalyzer For Weed? It’s Tied To A Car’s Ignition To Prevent Stoned Driving, Is This For Real?

Driving Simulation Study Highlights 

The researchers analyzed THC and its metabolite levels in both daily users and occasional users (no more than twice a week) and had a control group that didn't use marijuana at all. 

The scientists tested participants’ blood at baseline and then placed them in the driving simulator to drive for 30 minutes while measuring and assessing several aspects of their driving. Then the volunteers were given marijuana and asked to smoke "the amount you most commonly use for the effect you most commonly desire." After 30 minutes, researchers drew their blood and after another 15 minutes, the participants were back in the driving simulator. 

The results: 

• While the level of THC in the blood of the daily users after 30 minutes of consumption was about five times higher on average than the occasional users, daily users showed no statistically significant impairment, whereas occasional users showed evidence of decreased driving skills. 
• Scientists calculated two blood cannabinoid molar metabolite ratios and compared these to blood THC levels alone. 
• To confirm recent marijuana smoking, a cut point of 0.18 or higher for the molar metabolite ratio of THC to THC-COOH in blood showed 98% specificity (only 2% false positive rate), 93% sensitivity (7% of the times, the test will fail to detect recent use) and 96% accuracy (which combines the two rates) for identifying recent marijuana smoking. 
• In comparison, testing for THC alone provided 88% specificity, 73% sensitivity and 80% accuracy.

Kosnett explained that if an employer has a rule that workers can use marijuana at work, and a person’s molar metabolite ratio is above the cut-point, their boss can be confident (with 98% specificity) that the worker just used marijuana in the past 30 minutes.

Limitations 

One important limitation of this study is that the results don't show impairment, but only recent cannabis use. Kosnett added he and his team are working on a methodology that would help with identifying impairment. The study proves the method of identifying recent (30-minute) cannabis use, but it also discovered (though it was not its primary objective) different levels of impairment between regular and non-regular users.

Another limitation is that the study only measured levels 30 minutes after participants started smoking marijuana, and not everyone can get their blood drawn that quickly after an incident. That's why, the scientists are working on measuring metabolite ratios at different time intervals and with more participants. 

Continue reading at CU Anschutz Medical Campus. 

See Also: Caught Driving With THC In Your System? Here’s A Company You’ll Want To Know About

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