Chest-cavity fluid can provide a measurable cannabinoid metabolite when conventional specimens are difficult to obtain, but its THC-COOH concentration is not an interchangeable blood concentration or a clock for cannabis use. A 15-case autopsy study found THC-COOH in every chest-fluid specimen while leaving substantial uncertainty about specimen origin, postmortem change and quantitative interpretation.
Which cases and collection sites were studied?
Zughaibi and colleagues examined 15 selected cannabinoid-positive postmortem cases from Jeddah, Saudi Arabia, involving drug-related fatalities or criminal investigations. Fourteen decedents were male and one female; ages ranged from 18 to 50 years. The reported median postmortem interval was 48 hours, with case-table intervals from 24 to 320 hours.
Five cases were classified as non-putrefied, three partially putrefied and seven heavily decomposed. This was a selected case series, not a study of all deaths or all cannabis users. Thirteen cases involved other drugs.
Blood preserved with 1–2% sodium fluoride was collected from the subclavian vein, not the femoral vein. The text describes fluid from the chest or pleural cavity, but a figure caption also refers to chest and/or abdominal cavity fluid. That inconsistency limits how uniformly the fluid’s anatomical origin can be described. A pooled cavity specimen should not silently be relabeled peripheral blood.
What was measured in the chest fluid?
The investigators used solid-phase extraction followed by LC–MS/MS with labeled internal standards. THC-COOH was detected in all 15 cavity-fluid specimens, with a median of 480 ng/mL. Neither THC nor 11-hydroxy-THC was detected in that fluid.
The principal results give a THC-COOH range of 80–3010 ng/mL, while another table entry gives a minimum of 76 ng/mL. The inconsistency should remain visible rather than be converted into a single exact lower boundary. The series still demonstrates measurable metabolite in this alternative specimen.
The method used blood calibrators for chest fluid. The paper described calibration from 1 to 1000 ng/mL for fluids and a 1 ng/mL quantitation limit, with identification criteria including retention-time agreement within 0.05 minutes and ion-ratio agreement within 20%. It also described testing tenfold and hundredfold dilution. These method descriptions do not amount to a fully independent, matrix-matched validation for every possible decomposed cavity specimen.
Hydrolysis made some cross-specimen comparisons different
Chest fluid and preserved blood were prepared without hydrolysis. Urine, bile and gastric contents underwent alkaline hydrolysis before extraction. A hydrolyzed result can include analyte released from conjugated forms, so it does not necessarily measure the same fraction as an untreated specimen.
Consequently, a concentration difference cannot be attributed solely to anatomical distribution. Preparation also matters. This issue is illustrated separately by hydrolyzed urine and bile cannabinoid measurements after death.
The report contains inconsistent summaries of cavity-fluid ratios to other specimens. They do not provide a dependable divisor for estimating blood from a new chest-fluid value. Blood-site differences, small denominators and unequal preparation further limit such a conversion.
Decomposition was associated descriptively with higher values
Median cavity-fluid THC-COOH was 240 ng/mL in the five non-putrefied cases, 642 ng/mL in the three partially putrefied cases and 1100 ng/mL in the seven heavily decomposed cases. These are small descriptive groups. The paper did not supply a formal statistical test establishing the decomposition-stage pattern.
The authors proposed release from surrounding tissues, contamination, deconjugation and other postmortem changes as possible explanations. The study did not directly trace the source of the metabolite or measure each person’s concentration before death. It therefore cannot determine how much of an individual cavity-fluid result arose through a particular postmortem mechanism.
The authors also reported no significant relationship with the available drug-use history and no concentration difference by body mass index. These negative findings do not establish precise timing or exclude effects that a small selected sample could miss.
What the finding does not prove
THC-COOH is a metabolite finding, not a direct measure of psychoactive effect. Its detection cannot establish recent impairment, a consumed dose, or that cannabis caused the death. Absence of parent THC in cavity fluid likewise does not exclude prior cannabis exposure.
The useful inference is narrower: this fluid can preserve detectable metabolite under the studied circumstances. The specimen’s location, decomposition, preparation and calibration must accompany the result. Other alternative matrices, including muscle tested for THC and CBD, likewise require analyte-specific interpretation rather than automatic substitution for blood.
Primary source
Zughaibi TA, Alharbi H, Al-Saadi A, Alzahrani AE, Al-Asmari AI. 11-Nor-9-Carboxy Tetrahydrocannabinol Distribution in Fluid from the Chest Cavity in Cannabis-Related Post-Mortem Cases. Toxics. 2023;11:740. doi:10.3390/toxics11090740.
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