Sunday, August 2, 2015

Sandra Bland's Toxicology Report: THC

Sandra Bland’s toxicology report was released several days ago. The toxicology laboratory ran a basic "drugs of abuse panel" for several drug classes. The only results reported were blood THC concentration (18±4 ng/mL) and blood THC-COOH concentration (120±27 ng/mL). On a side note, the lab used GC/MS/MS to quantify THC, which is pretty cool to me. We don't see much gas chromatography tandem mass spectrometry in forensic toxicology.

I’m not going to interpret the blood concentration and offer an opinion on the matter because I do not have any additional information about the case. I do not have the facts and do not have a true context in which to place the toxicological findings. Currently, it is difficult to establish a relationship between a person’s THC blood concentration and impairing effects and it is not recommended to try and predict said effects based on blood THC concentrations alone.

But, I read a piece published by neuropsychopharmacologist Dr. Carl Hart, on the matter the other day and I found a few things that need clarified.

In his piece (found here), a few quotes were pretty bold. And a couple that were just wrong. I discuss these below. When I asked for a citation to the general Twitterati regarding Dr. Hart’s statements, Dr. Hart provided me with a citation to a paper by Cooper and Haney titled Comparison of Subjective, Pharmacokinetic, and Physiologic Effects of Marijuana Smoked as Joints and Blunts, published in the journal Drug and Alcohol Dependence. The full text paper can be found here open access.

The paper discusses plasma THC concentrations of subjects smoking marijuana. As mentioned before I’m not entertaining a discussion on actual concentrations or an opinion on the matter, but it is crucial to note the paper discusses THC plasma concentrations. The blood samples collected by the medical examiner were femoral and subclavian blood. They were not plasma. The reported blood to plasma ratio of THC is approximately 0.55 (range is 0.5-0.6). That is to say, blood concentrations should be approximately 55% of what plasma levels will be.

   A THC plasma level at 1 ng/mL is equivalent to 0.3 ng/mL in whole blood.
   A THC plasma level at 5 ng/mL is equivalent to 2.75 ng/mL in whole blood.
   A THC plasma level at 10 ng/mL is equivalent to 5.5 ng/mL in whole blood.
   A THC plasma level at 20 ng/mL is 11 ng/mL in whole blood.

Now, this is postmortem blood. It isn't antemortem blood. But taken at face value, a THC blood concentration of 18 ng/mL would equate to 32.8 ng/mL in plasma.

“Simply put, Waller County officials exaggerated Bland’s THC amounts.”

No, they did not exaggerate the amounts. They did [eventually] release the reports. They reported the correct values that were found. 18±4 ng/mL THC. Now, the interpretation of said results are a completely separate matter.

“Furthermore, the levels are far below the 150 nanograms per milliliter limit set by the World Anti-Doping Agency to indicate marijuana-induced performance alterations.”

The comparison of a postmortem whole blood THC concentration to the World Anti-Doping Agency’s (WADA) mandated THC-carboxylic acid metabolite concentration reporting threshold (150 ng/mL) is illogical and invalid. By doing this, one is not simply comparing apples to oranges. This is comparing apples to cats.

“It is disappointing that the county officials did not require him [Officer Encinia] to provide a urine sample for drug testing…”

It may or may not be protocol to do this. I do not know. But, even if it were, a urine drug test is negligible. It will more than likely provide little-to-no information about what was going on pharmacologically (if anything) in the officer’s body at the time of the traffic stop and eventual arrest. The detection of drugs in urine is typically measured in days. As an example, methamphetamine/amphetamine is detected in urine for approximately 1-5 days after administration. Heroin is detectable in urine as 6-acetylmorphine for up to 18-24 hours and as morphine for 1-4 days after administration. If you want more information on approximate drug detection windows, you can find it here. If one wanted to get a better picture or snapshot of what exactly was going on in the officer’s body at the time of the incident, then blood, not urine, would be the matrix to analyze.

One thing that wasn’t discussed in Dr. Hart’s piece, but I did see discussed in another article (with quotes from forensic toxicologists Dr. Bruce Goldberger and Dr. Nikolas Lemos) was postmortem redistribution (PMR).PMR is a phenomenon that occurs after death when drugs stored in tissues and organs diffuse back into the blood stream. This diffusion can falsely elevate the blood level at autopsy and may not be representative of the drug concentration at the actual time of death. THC can undergo PMR. In a series of 19 deaths, heart:femoral blood concentration ratios average 1.5 (range, 0.3-3.1) for THC. (Holland et al., 2010). In this case, femoral blood was analyzed, so PMR should be minimized, but it still can occur. If resuscitation was attempted (and I do not know if it was), then this could have also played a role in movement of blood from central to peripheral sites or even release of drug from tissues into blood creating a false elevation in blood drug concentration. Did PMR occur in this case? Unless a central blood sample was also analyzed (and quantified) for THC, we’ll never know. But it is something that must be taken into consideration when interpreting the postmortem blood THC concentration.
In postmortem toxicology, the entire case must be considered before offering an opinion on a matter. In the end, Sandra Bland did not die from a THC "overdose" or did not die from "THC intoxication". The blood THC findings do not change the ruled cause of death. All of this is just food for thought and things I thought should be clarified.




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