Postmortem Blood Sampling Sites: Interpretation Guide

Published by THE OKOROCHA FIRM*

A postmortem drug concentration is not necessarily the concentration that existed at the time of death. After circulation stops, drugs can move between tissues and blood, degrade, form from other compounds, or be affected by decomposition and storage. The measured result can therefore depend on where the specimen was collected, when it was collected, how it was preserved, and the properties of the drug.

What postmortem redistribution means

Postmortem redistribution is the collective term for site- and time-dependent changes in drug concentrations after death. Pelissier-Alicot and colleagues described several contributing mechanisms. Drug can diffuse from reservoirs such as the gastrointestinal tract, liver, lungs, and myocardium. Later, cell breakdown and putrefaction can release, degrade, or form compounds. Residual metabolism may also continue for a limited period.

Basic, lipophilic drugs with large apparent volumes of distribution are often considered more susceptible, but chemical properties alone do not predict every result. The authors emphasized analyzing specimens from different sites to recognize possible redistribution and reduce misinterpretation.

See Pelissier-Alicot et al., Mechanisms Underlying Postmortem Redistribution of Drugs (2003).

Central and peripheral blood are not interchangeable

Central and peripheral blood are not interchangeable. Central blood can be influenced by nearby organs that contained higher drug concentrations before death. Cardiac blood may receive drug released from the myocardium, lungs, liver, or stomach. Properly collected peripheral blood, commonly from a femoral site, is generally preferred for quantitative interpretation because it is farther from several major reservoirs.

Peripheral does not mean unaffected. The specimen collection technique matters. A blind vessel stick, blood pooled in a body cavity, or a mislabeled specimen can defeat the reason for requesting peripheral blood. The record should identify the anatomical site, whether the vessel was isolated or clamped, the collection method, the tube, preservative, specimen volume, and any contamination or trauma.

Gastric contamination can create a collection artifact

Logan and Lindholm examined gastric contamination of postmortem blood during blind-stick collection. Their work supports a narrow but important point: a reported blood concentration can be affected by the way the specimen was obtained when a needle or pooled sample is exposed to drug-rich gastric material.

This mechanism should not be assumed merely because a stomach contained drug. The review should identify the collection site and technique, whether the vessel was isolated, the condition of nearby tissues, the gastric contents, and whether independently collected peripheral blood or another matrix is available.

See Logan and Lindholm, Gastric Contamination of Postmortem Blood Samples During Blind-Stick Sample Collection (1996).

Matched and multi-site cases show why no universal factor exists

Pounder and Jones documented substantial site-related concentration differences in selected human cases. Hilberg, Rogde, and Morland compared available antemortem or early samples with later postmortem blood in a small heterogeneous case series and reported wide variation. These studies support preserving the anatomical source of every result and resisting a single central-to-peripheral correction factor.

Methamphetamine-specific reports reinforce the same limitation. McIntyre and colleagues compared antemortem whole blood with postmortem peripheral blood in three cases. Wurita and colleagues sampled multiple vessels, fluids, stomach contents, and tissues from one cadaver after a long postmortem interval. Both are useful observations, but neither study creates a universal multiplier for a different case.

See Pounder and Jones (1990), Hilberg, Rogde, and Morland (1999), McIntyre and colleagues (2013), and Wurita and colleagues (2016).

The preanalytical phase can change the result

Skopp’s review describes the preanalytical phase as a major determinant of postmortem toxicology quality. Relevant variables include specimen selection, collection, transport, registration, freezing, thawing, aliquoting, preservation, and specimen storage and stability. Autolysis and putrefaction can limit specimen usefulness. Formalin fixation or embalming can alter drug levels through dilution, matrix change, release, degradation, or chemical conversion.

This means analytical accuracy alone is not enough. A highly specific mass-spectrometric measurement can accurately quantify what was present in the submitted tube while leaving unresolved whether that tube represents the concentration at the time of death.

See Skopp, Preanalytic Aspects in Postmortem Toxicology (2004).

Drug stability and decomposition are compound-specific

Drummer reviewed postmortem issues involving amphetamines, cannabinoids, cocaine, opioids, and benzodiazepines. Some drugs or metabolites are unstable after death, while others may show increased blood concentrations through redistribution. Heroin markers, morphine glucuronides, cocaine-related analytes, and some benzodiazepines require particular attention to degradation and specimen handling.

The direction of change is not universal. A postmortem concentration can increase, decrease, or remain relatively stable depending on the drug, matrix, sampling location, postmortem interval, temperature, decomposition, and storage. A general statement that decomposition always raises or always lowers a drug level is not scientifically adequate.

See Drummer, Postmortem Toxicology of Drugs of Abuse (2004).

Why a lethal-concentration table is not enough

Ferner explained that many assumptions used in living clinical pharmacology become unreliable after death. Concentrations can vary unpredictably with sampling site and time. Published concentration ranges may also combine different matrices, collection methods, postmortem intervals, tolerance histories, co-intoxicants, and causes of death.

A numerical comparison can provide context, but it should not replace the complete investigation. Ferner cautioned that compilations labeled as lethal concentrations can be misleading when the underlying relationship between the fatal event and the later measurement is uncertain.

See Ferner, Post-mortem Clinical Pharmacology (2008).

Alternative specimens can test the interpretation

A complete postmortem examination can provide matrices that are unavailable in a living investigation. Depending on the analyte and question, useful specimens may include:

properly collected femoral or other peripheral blood;
central or cardiac blood, interpreted with its limitations;
vitreous humor, which is relatively isolated and useful for selected analytes;
urine, which may support prior exposure but not a blood concentration at death;
liver and other tissues, with matrix-specific reference and homogenization data;
gastric contents, which may support oral exposure but are vulnerable to sampling and diffusion issues;
brain, muscle, hair, bone, or other alternative matrices in selected cases; and
scene, prescription, hospital, emergency-treatment, and autopsy records.

Agreement or disagreement across matrices can be informative, but no single ratio provides a universal correction back to the concentration at death.

Records needed for a defensible review

scene history, body position, environmental temperature, and estimated postmortem interval;
autopsy report, diagrams, photographs, trauma, resuscitation, transfusion, and medical treatment;
the exact anatomical source and collection technique for every specimen;
tube type, preservative concentration, fill volume, seals, transport, and storage temperatures;
decomposition findings and any embalming, formalin exposure, freezing, or thawing;
screening and confirmation methods, analytes, calibration, controls, chromatograms, and repeat testing;
comparison specimens and tissue results; and
tolerance, prescriptions, prior drug use, co-intoxicants, and competing causes of death.

The careful conclusion

A postmortem result can reliably identify or quantify an analyte in the submitted specimen when the method is valid. It does not automatically recreate the concentration at the time of death. The opinion must account for the sampling site, postmortem interval, redistribution potential, stability, decomposition, preservation, treatment, tolerance, co-intoxicants, pathology, and alternative specimens. The most defensible conclusion explains both what the measurement supports and how postmortem processes limit the inference.

For related background, review biological matrices, vitreous humor toxicology, analytical methods, and toxicology data review.