A controlled animal experiment can show that postmortem change is biologically plausible without providing a correction factor for human autopsy blood. Hilberg and colleagues’ six-rat THC experiment is a useful example: the measured direction and magnitude depended on the vessel sampled, and the protocol differed substantially from human casework.
Six animals under a specific protocol
Male Wistar rats weighing 260–300 g were fasted overnight and given 30 mg THC mixed with 1 mL water by gastric tube. This was a fixed oral dose per animal, not a 30 mg/kg dose. Ninety minutes later, the animals were anesthetized and antemortem heart blood was collected. They were then sacrificed with carbon dioxide and left at room temperature for two hours before autopsy sampling.
Postmortem heart blood was drawn after clamping the inferior vena cava above the diaphragm. Vena-cava blood was collected after clamping above the renal veins; vitreous was obtained from both eyes. These controlled sites and intervals are essential to the result.
The vessel changed the finding
The mean postmortem-heart-to-antemortem-heart concentration ratio was 1.2 ± 0.1, expressed as mean ± standard error, and was not statistically significant. The postmortem-vena-cava-to-antemortem-heart ratio was 0.6 ± 0.1, a significant decrease (Wilcoxon P < 0.05). The postmortem-heart-to-vena-cava ratio was 1.9 ± 0.4 but was not significant.
These comparisons have different denominators and must not be collapsed into “THC falls 40% after death.” The significant 0.6 ratio compared a postmortem vena-cava specimen with an earlier heart specimen. It did not follow the same vena-cava blood through time.
The vitreous-to-antemortem-heart ratio was 0.12 ± 0.04 and significantly below one. This describes a different matrix, not a blood redistribution percentage. It does not validate vitreous as an interchangeable quantitative substitute.
What was measured analytically?
THC was quantified using capillary GC–MS with selected-ion monitoring and a deuterated internal standard. The stated blood calibration range was 0.001–0.305 μmol/L, with R² ≥ 0.997. The method was unsuitable for tissue analysis, so the rat results reported blood and vitreous rather than a complete set of tissue concentrations. Calibration linearity alone should not be represented as comprehensive validation for every matrix.
Why translation to human autopsy requires restraint
The oral route, fixed dose, species, short survival interval and two-hour room-temperature postmortem period all define the experiment. The authors specifically noted that human THC exposure commonly involves inhalation, which can alter initial tissue distribution. The experiment cannot resolve effects of days of decomposition or every human sampling technique.
The same paper included two human early-to-later blood comparisons with THC ratios in opposite directions. Their sampling sites also differed, and one case’s autopsy timing differed between narrative and table. Those cases are descriptive evidence of uncertainty, not validation of either a universal increase or decrease.
Accordingly, neither dividing a human result by 0.6 nor multiplying it by 1.2 is justified by this experiment. It did not test human impairment, crash causation or a fatal THC threshold. Our discussion of human central-to-peripheral ratios addresses a separate observational design; neither design supplies a universal antemortem reconstruction.
Primary source
Hilberg T, Rogde S, Mørland J. Postmortem Drug Redistribution—Human Cases Related to Results in Experimental Animals. Journal of Forensic Sciences. 1999;44(1):3–9. doi:10.1520/JFS14404J.
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