Postmortem urine and bile can support cannabinoid detection, but their concentrations cannot simply be read as blood concentrations or used as a clock for impairment. Saenz and colleagues examined 11 aviation fatalities and found useful qualitative results across non-blood specimens, without consistent concentration relationships to blood. Urine hydrolysis adds another essential distinction: the measured result includes material released from conjugates.
A small, selected series of aviation fatalities
The investigators selected 11 previously cannabinoid-positive cases from 2014–2015 with blood and most desired specimens available. All were male, aged 22–69 years. Urine was available in eight cases and bile in nine. These specimen denominators must remain separate from the total of 11 fatalities.
Blood was preserved with 1% sodium fluoride and 0.2% potassium oxalate; all specimens were stored at −20°C until analysis. Postmortem intervals were unknown. Blood collection sites were often undocumented; when provided in the laboratory’s casework, chest-cavity collection was common. The study’s blood comparator therefore cannot be uniformly relabeled as femoral blood.
Urine underwent hydrolysis
The method used solid-phase extraction and LC–MS/MS to quantify THC, 11-OH-THC and THC-COOH. Urine was incubated with beta-glucuronidase for three hours at 65°C before extraction to release glucuronide-bound material. A hydrolyzed urine result is analytically different from measuring only free drug in an untreated specimen.
THC and THC-COOH glucuronide controls were included, with results within 20% of target. An 11-OH-THC glucuronide standard was unavailable, so the corresponding hydrolysis control could not be included. That limitation matters when interpreting the completeness of metabolite deconjugation.
The distributions differed by analyte and specimen
Seven of eight urine specimens contained THC, ranging 1.25–32.2 ng/mL. All eight contained 11-OH-THC and THC-COOH, with ranges of 11.7–620 ng/mL and 24.2–970 ng/mL, respectively. These were hydrolyzed urine measurements.
Five of nine bile specimens contained THC, ranging 0.78–50.4 ng/mL. All nine contained 11-OH-THC and THC-COOH, ranging 0.98–227 ng/mL and 201–3307 ng/mL. Bile had the highest THC-COOH concentration within each case where it was available. A high bile concentration therefore cannot be assumed to indicate an equally high circulating concentration.
The reporting limit was a defined analytical choice
The method used eight calibrators spanning 0.78–100 ng/mL. Detection and quantification limits were administratively set at 0.78 ng/mL because it was the lowest tested calibrator meeting the identification and accuracy requirements. Lower concentrations were not evaluated to establish a lower validated reporting limit, and case results below the adopted limit were classified as negative.
Identification required retention-time agreement, product-ion ratio agreement and minimum signal-to-noise criteria. Dilution integrity was evaluated for concentrations above the calibration range. Thus, the quantitative findings involved a defined confirmatory procedure rather than a urine immunoassay screen.
Why detection does not date impairment
No consistent distribution between blood and any non-blood specimen was identified. Dose, route, frequency and time of cannabis use were unknown. There were no matched antemortem samples to show the concentrations before death, and the unknown collection intervals complicated assessment of redistribution.
The presence of 11-OH-THC, an active metabolite, should not be confused with proof of impairment at a particular earlier time. THC-COOH is an inactive metabolite, and its high concentration in excretory specimens is not a direct measure of psychoactive effect. The study did not establish crash causation or a fatal cannabinoid threshold.
Its strongest practical contribution is support for supplemental qualitative testing with transparent specimen and method labels. For the broader issue of alternative matrices, see why a useful screening specimen does not automatically replace blood.
Primary source
Saenz SR, Lewis RJ, Angier MK, Wagner JR. Postmortem Fluid and Tissue Concentrations of THC, 11-OH-THC and THC-COOH. Journal of Analytical Toxicology. 2017;41:508–516. doi:10.1093/jat/bkx033.
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