What Does a Toxicology Report Show After Death?

A postmortem toxicology report identifies the drugs, alcohol, poisons, gases, and other chemicals present in a deceased person’s body, along with how much of each substance was detected. The report draws on laboratory analysis of blood, urine, organ tissue, and sometimes less obvious specimens like the fluid inside the eye or even hair and nails. But the numbers on the report are not as straightforward as they sound, because death itself changes drug concentrations in ways that make interpretation far more complicated than a simple blood test on a living patient.

What Specimens Get Collected

During an autopsy, a forensic pathologist collects multiple types of biological samples for the toxicology lab. The most important are blood from the femoral vein (in the thigh), urine, vitreous humor (the gel-like fluid from the eye), stomach contents, and organ tissue from the liver and lungs.¹ Depending on the circumstances, other materials may be taken too: cerebrospinal fluid, bile, brain tissue, bone marrow, or skeletal muscle. The reason for collecting so many different samples is that no single specimen tells the full story. Each one reflects drug levels differently, and comparing concentrations across multiple sites helps the toxicologist piece together what actually happened.

Femoral blood is the gold standard because it sits relatively far from the major organs of the chest and abdomen, which makes it less vulnerable to a phenomenon called postmortem redistribution (more on that shortly).² Cardiac blood is also collected, but drug concentrations in heart blood tend to run higher than peripheral blood because drugs leach out of nearby organs like the lungs and liver after death. Urine, when present, is useful because it reflects what the kidneys had already filtered before death, giving a window into what substances the person used in the hours or days beforehand.

What the Lab Actually Tests For

The testing process typically starts with broad screening panels designed to flag the presence of common drug classes: opioids, benzodiazepines, amphetamines, cannabis, cocaine and its metabolites, barbiturates, and antidepressants. Early screening often uses immunoassay techniques, which are fast but imperfect. A study comparing immunoassay with a more advanced mass spectrometry method found that immunoassay produced a meaningful number of both false positives and false negatives, largely because of higher cutoff thresholds and interference from the biological matrix of postmortem specimens.³ For that reason, positive screening results are confirmed with more precise instruments, and many labs now run advanced mass spectrometry methods that can identify hundreds of individual compounds in a single analysis.

Beyond prescription and recreational drugs, the lab checks for alcohol (ethanol), carbon monoxide, cyanide, heavy metals like mercury and cadmium, and volatile chemicals like solvents or inhalants. If a specific poison is suspected based on the circumstances of death, additional targeted tests are ordered. The scope of testing depends partly on what the medical examiner or coroner already knows about the case: a suspected heroin overdose and a suspicious household death will prompt very different panels.

Why Drug Levels After Death Don’t Mean What They’d Mean in a Living Person

One of the trickiest parts of postmortem toxicology is that drug concentrations measured in a dead body do not correspond neatly to clinical blood levels in living patients. A review of published reference ranges found wide gaps between therapeutic serum concentrations used in clinical medicine and postmortem blood concentrations. For roughly a third of the drugs examined, the upper limit of the postmortem range was more than three times the upper limit of the therapeutic range.⁴ This means that seeing a drug level that looks alarmingly high on paper does not automatically mean the person was poisoned or overdosed. Conversely, a level that looks “normal” might not have been normal for that individual.

Separate research has confirmed that therapeutic plasma concentrations are of limited value when interpreting postmortem femoral blood results, and that postmortem-specific reference data should be used instead.⁵ The upshot for families waiting on a toxicology report is that the numbers alone don’t tell you the cause of death. A forensic toxicologist interprets those numbers in context, considering the person’s medical history, the circumstances surrounding the death, the autopsy findings, and the pattern of drugs across different specimens.

Postmortem Redistribution Changes the Numbers

After death, drugs don’t stay put. They move from organs with high concentrations into surrounding blood and tissue through passive diffusion, a process called postmortem redistribution. The lungs, liver, and heart are drug-rich reservoirs, and substances stored in those organs gradually seep into nearby blood vessels. This is why cardiac blood often shows inflated drug levels compared to blood drawn from the femoral vein in the leg.⁶

A Swedish study that compared drug concentrations across six different blood sampling sites in autopsy cases found that right heart blood levels averaged about 1.3 times the levels in the iliac vein (a peripheral site). Drugs that distribute widely through the body during life showed even larger differences between central and peripheral sites. Time since death mattered too: when the interval was long, arterial blood concentrations ran about twice as high as venous blood from the same region.⁷ The takeaway from this research is that blood collected sooner after death and from a peripheral vein gives the most reliable picture of what the person’s blood level was around the time they died.

Toxicologists use various markers and ratios to gauge how much redistribution has occurred. Comparing central blood to peripheral blood concentrations, or liver tissue to peripheral blood, helps them estimate whether a measured drug level is trustworthy or artificially elevated.⁶ None of these markers are perfect, but they give the toxicologist a sense of how cautiously to treat the raw numbers.

Vitreous Humor as a Protected Specimen

The fluid inside the eye turns out to be remarkably useful in postmortem work. Vitreous humor sits in an anatomically isolated compartment, which means it is far less affected by postmortem redistribution than blood is. It contains relatively few compounds that interfere with laboratory analysis, and its chemical makeup stays stable for a longer period after death.⁸

Vitreous fluid is also analyzed for electrolytes like potassium, sodium, and chloride, and for glucose. These biochemical markers help estimate how long someone has been dead and can flag conditions like diabetic crisis.⁹ For drug screening specifically, vitreous humor picks up fewer metabolites than urine does, but it successfully identifies a wide range of parent compounds, making it a solid backup when blood or urine is unavailable or compromised.¹⁰

Alcohol Is Especially Hard to Interpret

Ethanol is one of the most commonly detected substances in postmortem toxicology, but it’s also one of the hardest to interpret. The problem is that bacteria and yeast in a decomposing body can produce alcohol on their own. A person who never had a drink in the days before death can still test positive for ethanol if microbial activity has been active long enough. Higher alcohols, including 1-propanol and isobutanol, often show up alongside microbially produced ethanol and serve as markers that fermentation rather than drinking is the source.¹¹

Reliably separating alcohol consumed before death from alcohol produced after death requires a multi-marker approach, combining ethanol levels across different specimens with measurements of metabolites like ethyl glucuronide and ethyl sulfate.¹² Vitreous humor is especially valued here because its isolated location makes it less susceptible to microbial contamination than blood. Choosing the right specimen and storing it properly is critical for getting a meaningful alcohol result, particularly in bodies that have been dead for more than a day or two.¹³

What the Ratio Between a Drug and Its Metabolite Can Reveal

When your body processes a drug, enzymes break it down into metabolites. The ratio between the parent drug and its metabolites at the time of death can help toxicologists figure out whether a person took a single massive dose (acute overdose) or had been taking the drug regularly over time. In acute overdoses, the parent drug tends to be present in high amounts relative to the metabolite because the body hasn’t had time to break it all down. In chronic users, the metabolite levels are typically higher because the body has been processing the drug continuously.

This principle was demonstrated in a study of tricyclic antidepressant deaths, where the parent-drug-to-metabolite ratio in liver tissue was dramatically different in overdose cases compared to cases involving therapeutic use.¹⁴ However, these ratios aren’t always straightforward to read. Postmortem redistribution can alter the ratio for specific drugs in unpredictable ways. A person with a genetic variation that makes them metabolize certain drugs poorly could show a low metabolite ratio even at therapeutic doses. And drug interactions can slow or speed up metabolism in ways that muddle the picture.¹⁵

Carbon Monoxide and Other Gases

Not everything a toxicology report detects is a pill or a powder. Carbon monoxide poisoning is identified by measuring carboxyhemoglobin, the percentage of hemoglobin in the blood that has bound to carbon monoxide instead of oxygen. Levels above about 5% are flagged as potentially significant, and labs use both spectrophotometric methods and gas chromatography to measure it.¹⁶ This matters in fire deaths, furnace malfunctions, and suicides involving vehicle exhaust or charcoal burning.

Measuring carboxyhemoglobin in postmortem blood has its own complications. Decomposition can elevate methemoglobin, a form of hemoglobin that doesn’t bind carbon monoxide. If the analytical method doesn’t account for methemoglobin, it can report falsely high carboxyhemoglobin values. One laboratory found errors exceeding 50% with a standard gas chromatography method that failed to correct for methemoglobin, and developed a modified procedure using a reducing agent to eliminate the error.¹⁷ When blood is unavailable or too degraded, thoracic cavity fluid has been shown to correlate strongly with blood carboxyhemoglobin levels and can serve as an alternative specimen.¹⁸

Heavy Metals and Poisons

Toxicology reports can also reveal poisoning by heavy metals like mercury, cadmium, arsenic, and lead. These analyses are usually targeted rather than routine: a lab runs them when the circumstances suggest exposure, such as an unexplained death with symptoms consistent with heavy metal toxicity, or a suspected homicide. Postmortem tissue concentrations of metals like cadmium vary widely by organ, with kidneys typically showing the highest levels, followed by liver and intestine.¹⁹ Reference values for what constitutes a “normal” postmortem level versus a toxic one are still being refined, which makes interpretation challenging. For mercury specifically, newer analytical methods have proven faster and more reliable than older techniques, improving forensic labs’ ability to confirm mercury poisoning.¹⁹

Opioids and the Question of Tolerance

Opioid deaths present a particular interpretive challenge because the difference between a therapeutic dose and a lethal dose depends heavily on the individual’s tolerance. A blood morphine level that would be fatal to someone who never takes opioids might be unremarkable in a person with chronic pain who has been on high-dose opioids for years. This means the toxicologist needs to know, or at least estimate, the deceased person’s prior drug use history before calling an opioid level “toxic.”²⁰ Researchers have been looking for biological markers that could objectively indicate whether a person had developed opioid tolerance, which would make death investigations less reliant on incomplete medical records and witness accounts.

The role of genetics adds another layer. Variations in the gene for an enzyme called CYP2D6 affect how quickly a person metabolizes certain opioids. Someone who carries specific genetic variants may break down oxycodone much more slowly, leading to higher blood levels at a standard dose. A study that genotyped oxycodone fatality cases found that identifying CYP2D6 variants provided a more definitive explanation for the toxicity in several cases where the drug levels alone were ambiguous.²¹ This kind of genetic testing is not yet routine in every forensic lab, but it represents a growing area of postmortem investigation.

When Decomposition Complicates Everything

Bodies that are badly decomposed pose serious problems for toxicology. Bacteria break down some drugs entirely, making them undetectable even though the person took them before death. Other drugs are chemically altered by decomposition products in ways that confuse the analytical instruments. Putrefactive compounds extracted alongside drugs can mask signals or produce false readings, depending on the detection method used.²² The result is that a toxicology report from a badly decomposed body often carries wide uncertainty.

This is where alternative specimens become invaluable. Hair and nails are keratinized tissues that trap drugs and their metabolites as they grow. Because they resist decomposition far better than blood or soft tissue, they can reveal a person’s drug use history even when the body is severely degraded. A case report demonstrated that clozapine was detectable in both hair and nails from a decomposed body, confirming the deceased’s long-term medication use when conventional specimens were no longer viable.²³ Nail analysis in particular allows retrospective investigation of chronic drug exposure over weeks or months.²⁴

In extreme decomposition cases, even insects that have fed on the body can be tested for drugs and toxins. The field of entomotoxicology analyzes larvae and other insects recovered from remains to detect substances the deceased was exposed to before death.²⁵ The concentrations found in insects aren’t directly comparable to blood levels, but they can confirm that a drug was present in the body, which is sometimes the only evidence available.

How the Report Feeds Into Determining Cause and Manner of Death

A toxicology report by itself does not declare a cause of death. The medical examiner or coroner integrates the toxicology results with everything else known about the case: the scene investigation, the person’s medical history, the gross and microscopic findings from the autopsy, and the pattern of substances across different specimens. The toxicology report might show that a lethal combination of fentanyl and benzodiazepines was present, but the medical examiner still has to weigh whether those levels are consistent with lethality given the individual’s tolerance, body weight, and any underlying health conditions.²⁶

Distinguishing accident from suicide, or therapeutic misadventure from intentional overdose, often depends on details that the numbers alone cannot resolve. Whether the drug was injected, swallowed, or inhaled; whether the dose pattern suggests chronic use or a single acute ingestion; and whether the drug levels are consistent with the behavior witnesses described in the person’s final hours are all factored in. The toxicology report provides critical evidence, but it is one piece of a larger puzzle.

Embalming Artifacts

When a body has been embalmed before an autopsy is ordered, the toxicology results can be contaminated in ways that look like poisoning. Embalming fluids typically contain formaldehyde, methanol, sodium borate, and other chemicals that mix with the body’s fluids and tissues. Vitreous humor that turns pink is a telltale sign that embalming fluid has reached the eyes. In one reported case, methanol was detected in a subdural blood clot from an embalmed 87-year-old woman. The finding initially raised questions about methanol poisoning, but further investigation showed the methanol came from the embalming fluid, not from anything the woman consumed.²⁷ Labs experienced in postmortem work know to flag results from embalmed bodies and interpret them with extra caution, but it remains a real source of confusion, especially in cases where the death is reported to the coroner’s office only after funeral preparations have begun.

Why Reports Take So Long

Families waiting for a toxicology report are often told it will take weeks or even months. This timeline frustrates people, but there are practical reasons for it. Comprehensive drug screening requires multiple analytical steps: initial immunoassay screening, confirmatory testing by mass spectrometry, quantification of identified substances, and sometimes additional specialized tests for metals, gases, or unusual poisons. Each step takes time, and forensic laboratories typically handle a heavy caseload with limited staff. Specimens may also need to be sent to reference laboratories for specialized analyses that the local lab cannot perform. The toxicologist’s interpretive report, which contextualizes the raw numbers, adds additional time. In complex cases involving multiple drugs or unusual circumstances, the interpretation itself requires careful review of the scientific literature and consultation with the medical examiner. The delay is not a sign that something went wrong — it reflects how much work goes into getting the answer right.