Study finds postmortem THC tests don’t shed light on intoxication levels before death

Was that driver under the influence of marijuana when she crashed into another car and died? Was that parolee flying high on weed when he was killed in a shootout with police?

The short answer, according to new research conducted at the El Paso County Coroner’s Office: We’ll never know.

The state of Colorado says drivers are impaired if their blood tests at 5 nanograms per milliliter or more of Tetrahydrocannabinol (THC), the psychoactive component of marijuana. At that level, they could be charged with driving under the influence of drugs.

But it gets trickier after a person dies. The study, conducted by Andrea Tully, the coroner’s assistant toxicologist, found that postmortem testing for THC is unreliable, and it’s impossible to prove scientifically whether a person was high or impaired before they died.

Tully notes, “More decomposed specimens would see higher levels of THC. Thus, we can’t really rely on postmortem THC concentrations when it comes to the impairment level that somebody was at, or the level that they had in their system, when they were alive.”

So while a test for THC on a corpse will give a reading, Coroner Dr. Leon Kelly says, “That number on the page doesn’t mean anything.”

The study found that the reason for the bad readings is related to how a body’s decomposition affects THC levels. It’s worth noting that the same isn’t true for alcohol — its concentration in blood doesn’t change postmortem.

The THC finding could have implications for what can and can’t be documented in civil courtrooms where attorneys try to prove someone was impaired by THC and, therefore, liable for injury or death in traffic crashes or other incidents, Kelly explains.

But, he cautions, “This is a whole new world, and we’re sort of figuring out in real time what this means and what to do with it.”

After serving an internship at the Coroner’s Office six years ago led to a full-time job, Tully sought a master’s degree in chemistry from the University of Colorado at Colorado Springs and chose to conduct the study as her master’s thesis.

To carry out her study, Tully sought to measure postmortem effects on concentrations of THC and its metabolites, which are compounds produced from chemical changes of a psychoactive substance in the body.

“I undertook this work primarily due to the fact we were lacking in this area of analyzing blood samples for THC,” Tully says. “Since marijuana is becoming more and more legalized, it’s important for us to be able to do analyses in blood, put numbers on things, especially with the DUI limits. I don’t think many other places did blood THC [quantification], and it’s important to get with the times.”

Kelly says he encouraged her, saying the study isunique and comes at a time when marijuana’s legality is becoming more prevalent across the country and there’s growing interest in the impact of weed on crime, vehicle crashes and suicides. Medical marijuana is legal in 33 states, and 11 states, including Colorado, have legalized recreational marijuana. (Both are also legal in Washington, D.C.)

[pullquote-1] Kelly says more and more he was being asked to decide whether marijuana played a role in a death. “But,” he says, “we couldn’t really answer that question, given what we were testing. And so we decided that would be a great project for [Tully] to do her thesis on — an analysis of marijuana metabolites and seeing what that can tell us about the circumstances in which people are dying. Do those [metabolites] really reflect the level of those drugs in life?”

Kelly explains that a certain percentage of drugs, whether recreational or therapeutic, get sequestered in the liver or lungs or other organs where they bind with proteins in the body and become inactive.“So what happens after death, though, is the proteins starts to break down, and they release that drug back into the body,” he says. “And then, when you take the sample after death, the drug will shoot sky high, and you think, ‘Oh, my God.’ But in fact, that’s a postmortem artifact. It’s just the process of death.”

Tully says she tested numerous blood samples from more than 100 bodies for her study. She looked at levels of both “parent THC,” the drug itself which gets broken down and dissipates from the blood within a few days, though it’s stored in a body’s fat, and THC metabolites, the byproduct of the body breaking down THC, or metabolizing, which can linger longer in the blood.

“I didn’t just look at one sample of blood,” she says. “I looked at a bunch of samples that we drew from one person. So, say, during the autopsy, they drew blood from a femoral site, cardiac site, you know, all these different areas of the body.”

Tully captured blood in various conditions as well, such as soon after death if a patient was in a hospital, which she described as “really pristine, nice blood.”

“But sometimes, you know,” she says, “when we get the blood from postmortem autopsy, the draws aren’t as clean. They can draw up some fat as well. Sometimes the person can be decomposed, so there’s lots of fat and oils mixed in with the blood.

“So I would look at a sample that was drawn right when the body got here versus several hours later at autopsy and see if there was a difference,” she says.

Tully then took all the samples — ranked excellent, fair, poor and decomposed — and created statistical graphs of varying factors and concentrations.

The findings didn’t all match her expectations. For instance, she expected to find the blood from the central areas of the body would contain higher levels of THC (since it can be stored in those organs) than the peripheral areas. Interestingly, that wasn’t the case.

Another finding did make sense. She looked at the blood’s parent THC concentration over time. “I found that the worse our sample condition is, the higher the concentration of THC,” she says. “So if I get a really fresh, good sample of blood, say, from the hospital, those levels of THC would be lower versus from a really decomposed specimen — those levels would be sky-high.”

THC metabolites, on the other hand, didn’t display statistical significance due to time. Tully says that makes sense, because parent THC is a highly lipophilic drug, meaning it “hangs out in the fat,” and therefore, the older the blood gets, the more it takes on fat and oil from the body, making THC levels rise. The THC metabolite is hydrophilic, or water soluble, and is discharged from the body through various pathways and not held in the fat.

While that seems to contradict the theory that parent THC dissipates quickly, Tully explains that although parent THC has a very short half-life, it can be and is stored in fat, which prolongs its appearance.

Werner Jenkins, chief toxicologist with the Coroner’s Office, noted that for the study, in some cases, blood samples were obtained from subjects who were still alive at the hospital, and showed a lower-than-legal-limit of intoxication — below 5 nanograms per milliliter. But blood taken at autopsy showed higher levels.

If and how the study will impact the real world of litigation is unclear.

H. Zachary Balkin, managing attorney with Frank Azar & Associates in Aurora, declined to comment, saying he’d reserve judgment pending a review of the study.

But Mike McDivitt, founder and CEO of McDivitt Law Firm, tells the Indy the findings could be pertinent in denying a litigator conclusive proof, and thus an aggravating factor in a case, that a negligent driver was impaired by THC. Aggravating factors can push court or jury awards higher in wrongful death and injury cases.

But he says he’s not too worried, because usually there’s other evidence of liability contained in police reports of crashes from which jurors could conclude who’s responsible for injury or death.

“I don’t think it’s a negative factor in pursuing wrongful death claims,” McDivitt says.

The Colorado Springs Police Department, El Paso County Sheriff’s Office and 4th Judicial District Attorney’s Office declined to comment until officials have studied the research.

But Kelly notes that the study will impact his testimony as a witness: “I can’t go to court and ultimately, with confidence, say that this postmortem level of marijuana really indicates beyond any reasonable medical certainty that the victim was intoxicated.”

The impact for Kelly isn’t just legal — families of suicide victims, for instance, often want to know if intoxication could have played into those final moments. Unfortunately, he says, he won’t be able to answer those questions.

“My concern is what’s true, and what’s honest, and what’s scientifically reliable,” he says. “This work that we did here is critical to knowing what we can and can’t say.”

The study could have widespread impacts — if it gets attention. Tully hopes the Journal of Analytical Toxicology will publish her 85-page thesis, titled, “Examination of Concentrations of THC and Its Major Metabolites in Postmortem Blood Using Solid-Phase Extraction Preparation Methods and Analysis by Liquid Chromatography-Tandem Mass Spectrometry.”

Meantime, Jenkins says he and Tully are continuing to collect samples and adding to the THC data. Tully has also launched another project. She’s developing a screening procedure to detect various types, or analogs, of fentanyl, a deadly synthetic opioid whose properties are constantly being altered by manufacturers to sidestep import bans.

Jenkins says Tully identified an analog that hadn’t yet been cataloged by the National Medical Services lab in Philadelphia, which serves El Paso County and many other coroner’s offices in the U.S.