Postmortem Toxicology: Can the Dead Tell Their Stories? - Expert Article

Forensic toxicologists are often called upon to determine whether drug or alcohol intoxication was a contributing factor to a vehicle crash, workplace injury, or other fatal incident. In this article, Dr. Vanessa Fitsanakis discusses the process of conducting a postmortem toxicological analysis to determine drug and/or alcohol concentrations.

Postmortem Toxicology: Can the Dead Tell Their Stories? - Expert Article

Autopsies are systematic medical inspections that occur after death (postmortem). Their purpose is to address questions about the cause of death of the individual. [1] A family member or physician may request a clinical autopsy to substantiate the cause of death, assess antemortem healthcare, or verify that the death was not due to a public health threat. [2] Law enforcement professionals may request a medicolegal autopsy if someone dies under suspicious circumstances. [1, 2] In 2007, the most common reason for performing an autopsy was to determine death following an assault (Figure 1). The autopsy may also involve obtaining a postmortem sample for a toxicology screen.

FIGURE 1. Most Commonly Autopsied Causes in the U.S. in 2007. These data are in the public domain through the Centers for Disease Control National Hospital Care Survey, National Vital Statistics System, Mortality section.

At times, lawyers may ask forensic toxicologists to review the postmortem toxicology report and provide an opinion regarding the postmortem drug or alcohol concentrations. The central question is often whether the concentrations indicate antemortem intoxication or impairment. In some cases, the toxicologist is asked to determine whether the postmortem levels of drugs, alcohol, or other chemicals reflect therapeutic, toxic, or lethal concentrations. On the surface, these questions seem like they should have simple answers. In reality, interpreting postmortem drug and alcohol levels can be quite complex and requires careful examination and analysis by experts.

The National Association of Medical Examiners (NAME) publishes standards for performing forensic autopsies, including the collection of postmortem samples for toxicological analysis. Adherence to these standards is not mandatory, but they do provide a foundation on which forensic pathologists are encouraged to build their practice. [3] These standards also outline information for how medical examiners may collect and submit samples for postmortem toxicology screens. It is particularly important to specify the anatomical location from where the sample was obtained. This is because femoral (leg) blood from a peripheral compartment (PC) may have a different drug or alcohol concentration than cardiac (heart) blood from the central compartment (CC). These concentrations may also differ from those obtained from urine (PC), vitreous humor/eye (PC), stomach (CC) or chest cavity blood (CC) samples (Figure 2).


Postmortem Redistribution (PMR)

Depending on the drug, apparent differences in concentrations could be due to a process called postmortem redistribution (PMR). PMR refers to the change in postmortem drug blood concentrations of specific chemicals that may occur due to movement of that chemical from an area of higher concentration to one of lower concentration (Figure 3).

Chemicals move from regions of high concentration (left) to those of low concentration (right). This holds true after death as well.
Chemicals move from regions of high concentration (left) to those of low concentration (right). This holds true after death as well.

This process is thought to primarily occur between organs in the central compartment (torso), but not in the peripheral compartment (legs/arms). When a person dies, normal biological functions cease, and some chemicals may migrate out of the tissue or organ where the drug/chemical was stored or where it was present, and move into the blood or other organs in close anatomical proximity (Figure 4). Hence, PMR could result in an increased postmortem drug concentration in a central compartment derived sample that is not representative of its antemortem concentration.

Antemortem drug or alcohol from the stomach (high concentration) could accumulate in the pericardial sac (low concentration) along with the pericardial fluid. Care must be taken during autopsy to remove blood from the heart, and not the pericardium, to provide a more accurate reflection of antemortem drug or alcohol levels. Analysis of pericardial fluid may provide a toxicological sample with alcohol levels that do not accurately reflect antemortem BACs.

Determining Antemortem Concentrations

PMR does not always occur, however. This is because each chemical has unique properties that govern the tendency of that chemical to undergo PMR. Forensic toxicologists, therefore, do not solely rely on the toxicology report to assess antemortem concentrations. Rather, they use their education, training, and/or experience to analyze the specific chemical in question. This includes information about the chemical’s propensity to undergo PMR, data about events leading up to the death, the state of the body at autopsy, and the time between death and autopsy (postmortem interval). A careful evaluation of the case involves consideration of multiple factors, rather than relying solely on the postmortem chemical level.

Finally, a toxicologist may also evaluate the medical and prescription history of the deceased. For example, if the postmortem toxicology report indicated a high blood concentration of a prescription drug, several scenarios could explain this. (1) The person may have been in the hospital and received an intravenous injection of the drug immediately preceding death. (2) The person may have had a substance use disorder that resulted in consumption of high doses of the drug. (3) The person’s physician may have prescribed high therapeutic doses of the medication. (4) The person may have ingested a lethal dose, either accidentally or purposely. In the absence of past medical and prescription history, it would be difficult for a forensic toxicologist to distinguish among the above options.

FORENSIC TOXICOLOGY INVESTIGATIONS

Questions related to postmortem levels of drugs or alcohol often focus on whether these chemicals contributed to death, or whether the levels indicate antemortem intoxication or impairment. To answer these types of questions, it is essential to collect and analyze multiple types of relevant information. This approach enables the toxicologist to consider postmortem drug, alcohol, or other chemical levels in the context of the specific case.

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