The number of drug tests in Illinois that turn up positive for marijuana is on the rise, even before adult use is set to become legal beginning Jan. 1.
Data from drug testing company Quest Diagnostics found 3.1% of urine specimens from the general Illinois workforce tested positive for marijuana in 2018, up from 2.2% positive in 2014.
The company compiled data from roughly 1.5 million tests conducted in the state during the past five years.
But Dr. Barry Sample, director of science and technology, said the number of tests employers here order could decrease once legal use begins.
That's because the inclusion rate of marijuana in preemployment drug screens has decreased in states where recreational use is legal.
In 2018, according to Quest data, 97.6% of preemployment tests nationwide included marijuana, while 94.7% did so in states with permitted recreational use.
The decrease comes because of the purpose of preemployment testing, which employers can conduct under an Illinois workplace privacy act to screen for use of illicit substances but not legal ones, said Mary Lynn Fayoumi, president and CEO of Downers Grove-based HR Source.
"It prohibits employers from discriminating against employees for their off-the-job use of lawful products," Fayoumi said. "And cannabis now will be a lawful product."
Even if preemployment tests for marijuana decrease, testing for other reasons is expected to continue.
Sample said random testing is not as common and makes up only 15 to 16 percent of the tests the company conducts.
But employers may see the need for random testing to ensure compliance with zero-tolerance drug policies, which remain legal and enforceable even once recreational cannabis use begins.
Sample said employers also will continue reasonable suspicion testing, to determine whether an employee suspected of intoxication was indeed impaired on the job; and post-accident testing, to investigate the reasons for a workplace injury, crash or other incident.
Urine tests will continue to be the most common method of detecting marijuana use, Sample said. Oral swabs using saliva and hair tests aren't as reliable or definitive, he said.
"Urine detects recent use. Oral detects relatively recent use," Sample said. "Hair detects a pattern of repeated use."
Drug testing firms also will continue to use two rounds of lab testing before reporting a positive result, an initial and a confirmatory.
Each comes with a different threshold that must be met in order to indicate marijuana use.
The initial threshold Quest uses is 50 nanograms of THC (tetrahydrocannabinol, the psychoactive component of cannabis) per milliliter of blood; the confirmatory threshold is 15 nanograms per milliliter.
For the casual user, marijuana no longer would be detectable at these levels in the bloodstream within two to three days after use, Sample said.
However, Dr. Gregory Teas, an addiction expert and psychiatrist at Amita Health in Hoffman Estates, said marijuana is fat-soluble and is metabolized at different rates by every person's system. It deposits in fatty tissue and can be released into the blood over time.
"Individuals who are overweight are more likely to test positive for longer periods of time in the urine," Teas said.