Tox Tuesday: Per se laws and roadside drug testing

An estimated more than 10 million U.S. drivers (around 5% of licensed drivers in the entire country) drove under the influence of an illegal drug within a year period, according to a 2007 study by the U.S. National Survey on Drug Use and Health. Now, we all know what happens if a suspected drunk driver is pulled over: out comes the breathalyzer. But what if a driver is intoxicated with a drug other than alcohol, for which breathalyzers don’t work?

To keep roads safe — especially as drug laws change around the world, with marijuana being legalized in more locations — law enforcement officials and other experts must answer a lot of questions as they devise DUID (Driving Under the Influence of Drugs) laws. How should they test drivers for drugs? What kind of tests should they use? What levels should they test for? Answers don’t come easily.

Per se laws

The term “per se law” comes up a lot in these discussions. The Canadian Centre on Substance Abuse defines the phrase as a “law whereby it is an offence to operate a vehicle with a concentration of alcohol or drugs in the body in excess of a specified threshold value.” To many governments, that threshold is zero.

Why zero? Because so far, it’s been difficult to identify an exact threshold at which a substance like THC, the main compound in marijuana, can be detected in the body that is suitably indicative of intoxication.

With alcohol, it’s simple to determine a blood-alcohol percentage that denotes impairment. It’s harder to come up with a level of impairment for other substances, however, for many reasons related to the chemistry of how the body breaks down substances. As a result, under many per se laws, drivers are forbidden from hitting the roads if a drug or drug metabolite is present at any detectable level in the body.

Many argue that per se laws will incriminate drivers who aren’t intoxicated when they’re pulled over. For example, THC can be detected in the body days or weeks after consumption (exactly how long depends on the type of test, threshold of detection targeted, regular or singular substance use, and other factors), so a driver who tests positive for marijuana may have used the drug long before operating a vehicle, when the effects of the drug have already worn off.

Some drivers may have ingested a substance as part of a prescription, meaning drivers who test positive could be held in custody while awaiting medical review of the circumstances behind the usage. Others may have ingested a drug through secondhand smoke exposure.

The best way to test?

Oral fluid roadside testing is in its early stages in many parts of North America and Europe. The tests can detect recent usage and are relatively non-invasive, but development is new, and it will take time for law enforcement to have reliable methods and data to reference. But unlike blood and urine tests, oral fluid tends to target parent drugs instead of metabolites processed by the body. Because metabolites remain in the body for a longer period of time than the parent drug, oral fluid tests detect more recent usage.

Oral fluid, however, is a relatively new testing matrix, compared to blood and urine. The laws and cutoffs surrounding an impairment threshold are still in flux regarding oral fluid, whereas the methods for urine tests have been long established. This makes legislation based on oral fluid tests hard to nail down.

Blood and urine tests can detect a number of drugs, but these tests aren’t always practical. They involve transporting a suspect, sometimes to a medical facility. Blood screening typically looks for both parent drugs and metabolites, but uses more sophisticated equipment and quick results aren’t a priority.

So, the trick with oral fluid testing is to make a testing method that is rapid, scientifically defensible, and easy enough for a hypothetical police officer to use after dark, in the rain, with a suspect who isn’t enthusiastically cooperating. No small task.

Forensic science is catching up, as culture changes and drugs become more accessible. Law enforcement will always be trying to find reasonable methods to keep the streets safe. In the future, perhaps oral fluid can allow the law to confirm DUIDs in a way that fits in with changing drug laws.

For information on Neogen’s toxicology solutions, which include drug detection assays and oral fluid collection tools check out our website.

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