An autopsy toxicology report lists every substance detected in a deceased person’s body, the concentration of each substance, and which body fluid or tissue was tested. Reading one can feel overwhelming, but each section follows a consistent logic: what was found, how much was found, and where in the body the sample came from. Understanding these three elements is the key to interpreting the entire document.
The Layout of a Typical Report
Most toxicology reports begin with identifying information (the decedent’s name, case number, date of death, and date of analysis) followed by a table or series of tables. Each row in the table typically lists a substance, the specimen it was found in (such as blood, urine, or vitreous humor), the concentration measured, and sometimes a note about the testing method used. Some reports also include a brief narrative from the toxicologist summarizing the findings.
At the bottom or in a separate section, you’ll often see a list of substances that were screened for but not detected. This matters more than it seems, and we’ll get to why below.
Why the Specimen Type Matters
The single most important detail on a toxicology report is which body fluid was tested. You’ll commonly see blood (sometimes labeled “femoral blood” or “heart blood”), urine, vitreous humor (fluid from the eye), bile, and sometimes liver tissue or stomach contents. These are not interchangeable, and the same drug can show very different concentrations depending on where the sample was taken.
Peripheral blood, drawn from the femoral (thigh) vein, is considered the most reliable specimen for measuring drug concentrations. Central blood, drawn from the heart or nearby vessels, tends to show higher concentrations. Research comparing different collection sites found that drug levels in heart blood averaged about 1.3 times higher than in femoral vein blood. This difference isn’t because the person had more of the drug in their heart. It’s an artifact of what happens after death.
If you see “femoral blood” or “peripheral blood” on a report, the numbers are generally more trustworthy for estimating what was in the person’s system at the time of death. If the report only lists “heart blood” or “cardiac blood,” keep in mind those concentrations may be artificially elevated.
Vitreous Humor
Vitreous humor is the gel-like fluid inside the eyeball, and it appears on toxicology reports more often than people expect. It’s tested because the eye is relatively sealed off from the rest of the body, making this fluid resistant to bacterial contamination and the chemical changes that happen during decomposition. For alcohol in particular, vitreous humor is extremely useful. Alcohol concentrations in vitreous humor remain stable after death for a longer period than in blood, and the fluid is far less prone to the post-mortem alcohol production that can falsely elevate blood alcohol levels. When a body has been decomposing, vitreous humor may be the most reliable specimen available.
Understanding the Units
Drug concentrations on toxicology reports are expressed in units that describe weight per volume, essentially how much drug is dissolved in a given amount of fluid. The most common units you’ll encounter are:
- ng/mL (nanograms per milliliter): used for potent drugs found in tiny amounts, like fentanyl or benzodiazepines. One nanogram is one billionth of a gram.
- mcg/mL or µg/mL (micrograms per milliliter): used for drugs present in larger quantities, like acetaminophen or anticonvulsants. One microgram is one millionth of a gram, so 1 µg/mL equals 1,000 ng/mL.
- mg/L (milligrams per liter): numerically identical to µg/mL. If you see one, you can treat it as the other.
- g/dL (grams per deciliter): used almost exclusively for blood alcohol concentration. A BAC of 0.08 g/dL is the familiar legal limit for driving.
The scale differences matter. A fentanyl level of 5 ng/mL and an acetaminophen level of 5 µg/mL are not comparable quantities. The acetaminophen concentration is 1,000 times higher. Always check the units before comparing numbers across substances.
What “None Detected” Actually Means
Every lab instrument has a detection limit, the smallest amount of a substance it can reliably identify. When a report says “none detected” or “negative,” it means the substance was not found at or above that detection limit. It does not guarantee the substance was completely absent. A person could have had a low concentration of a drug in their system that fell below the lab’s threshold.
Equally important: the report only covers substances that were specifically tested. The Virginia Department of Forensic Science notes that a clean result “does not exclude the presence of drugs in categories not tested.” If a particular drug wasn’t included in the screening panel, it won’t appear on the report at all, whether it was present or not. If you suspect a substance was involved but don’t see it listed, check whether it was part of the testing panel, which is sometimes listed separately.
You may also see the term “trace” or a result noted as “below the limit of quantitation.” This means the lab detected the substance but couldn’t measure the exact amount. The drug was there, just in a quantity too small to put a reliable number on.
Screening Tests vs. Confirmatory Tests
Toxicology testing happens in two stages. The initial screening uses a rapid, relatively inexpensive method called immunoassay to flag which substances might be present. These tests cast a wide net but can produce false positives because structurally similar compounds sometimes trigger the same reaction.
Any positive result from screening gets sent to a confirmatory test, most commonly gas chromatography-mass spectrometry (GC-MS). This method physically separates each compound and identifies it by its molecular structure, making false positives extremely rare. If a substance appears on the final report with a specific concentration, it almost certainly went through confirmatory testing. Some reports explicitly note the method used next to each result.
Therapeutic, Toxic, and Lethal Ranges
Many people reading a toxicology report want to know one thing: was the amount of this drug dangerous? Forensic toxicologists use three general categories to frame drug concentrations. Therapeutic range refers to concentrations seen in people taking a drug as prescribed, with minimal side effects. Toxic range describes concentrations associated with clinically significant symptoms or poisoning. Comatose-fatal range covers levels reported in cases of coma or death.
These ranges are published in reference databases and textbooks, and if you search for a specific drug’s name along with “therapeutic toxic lethal concentration,” you can often find the reference values. However, comparing a number on a report to a published range requires serious caution for reasons explained in the next section.
Post-Mortem Redistribution Changes Drug Levels
This is the concept that trips up most non-specialists. After death, drugs don’t stay where they were. They migrate. Organs like the liver, lungs, and heart act as drug reservoirs during life, storing high concentrations. After death, those drugs passively diffuse out of the organs and into surrounding blood vessels and tissues. Cells break down, releasing their contents. Blood pools and shifts with gravity. Bacteria begin to degrade some compounds and, in some cases, produce new ones.
The result is that post-mortem drug concentrations can be significantly higher than what the person experienced while alive. This is especially true for drugs that are fat-soluble or that distribute widely into tissues during life. Drugs with a high “volume of distribution,” a pharmacological measure of how much a drug spreads beyond the bloodstream, are the most prone to post-mortem redistribution. Many common medications fall into this category, including certain antidepressants, antipsychotics, and opioids.
This is why a toxicology report number cannot simply be compared to a chart of lethal doses and treated as definitive. A blood concentration that looks lethal on paper may have been pushed into that range by redistribution, not by the amount the person actually took.
Interpreting Alcohol Results
Alcohol is one of the most common findings on toxicology reports and one of the trickiest to interpret. The number is reported as a blood alcohol concentration (BAC) in g/dL. For context, the legal driving limit in most U.S. states is 0.08 g/dL.
The complication is that bacteria naturally produce ethanol during decomposition. A body that sat for hours or days before testing can show a positive BAC even if the person hadn’t been drinking. This is why reports often include alcohol results from both blood and vitreous humor. If both specimens show similar alcohol levels, the result is more reliable. If only the blood is positive and the vitreous is negative or much lower, post-mortem alcohol production is a likely explanation. Research has also found that post-mortem BACs tend to be lower than the person’s actual BAC at the time of death, with one study showing a median post-mortem BAC of 0.06 g/dL compared to 0.10 g/dL measured before death in the same individuals.
Fentanyl as a Case Study in Interpretation
Fentanyl illustrates why toxicology numbers alone can’t tell the whole story. In a study published in the Journal of Medical Toxicology, researchers examined post-mortem fentanyl concentrations across different causes and manners of death. Among accidental deaths related to substance use, blood fentanyl ranged from 1 to 102 ng/mL. Among people who died of natural causes while on prescribed fentanyl, levels ranged from 1 to 78 ng/mL. In suicides, the range was 3 to 462 ng/mL.
The overlap is striking. A person with a fentanyl level of 15 ng/mL could be someone who died of an overdose or someone with chronic pain and significant opioid tolerance who died of something entirely unrelated. The researchers noted they could not assess individual tolerance levels, and that an opioid-naive person and a long-term fentanyl user would display very different responses to the same blood concentration. This is why cause of death is determined by the medical examiner using the full picture (autopsy findings, medical history, scene investigation, and toxicology together), not by any single number on the toxicology report.
Putting It All Together
When you sit down with an autopsy toxicology report, work through it systematically. Start by identifying which specimens were collected and focus on peripheral blood results as the most reliable. Check the units for each substance so you’re comparing numbers on the correct scale. Note what was tested and not detected, not just what was found. Look at whether vitreous humor was tested alongside blood, particularly for alcohol, since matching results between the two specimens increase confidence in the findings.
For any substance detected at a specific concentration, remember that post-mortem redistribution means the number you see may not reflect what was circulating in the person’s blood at the moment of death. Published therapeutic and lethal ranges can provide a rough frame of reference, but they were largely established in living patients, not post-mortem specimens. The forensic pathologist and toxicologist who wrote the report have already factored these complexities into their conclusions, which is why the narrative summary, when included, is often the most useful part of the entire document.