An evaluation of postmortem concentrations of Δ9-tetrahydrocannabinol (THC) and 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (THCCOOH)

Abstract

Δ9-tetrahydrocannabinol (THC), the primary psychoactive component of cannabis, leads to impaired cognitive and psychomotor function resulting in an increased risk of fatal motor vehicle collisions and other traumas resulting in death. It is important to measure cannabinoids in postmortem cases to improve understanding of this growing public safety issue. However, postmortem concentrations of THC and its primary inactive metabolite, 11-nor-9-carboxy-tetrahydrocannabinol (THCCOOH), have not been extensively studied. We aim to further characterize postmortem concentrations of THC and THCCOOH in peripheral blood with and without preservation, central blood, and central “serum” to support improved forensic interpretation. Cannabinoids were extracted from blood and “serum” from twenty-five decedents using solid phase extraction followed by quantification using gas chromatography – mass spectrometry. We evaluated the impact of sample preservation, reported central blood-to-peripheral blood (CB:PB) ratios and blood-to-”serum” ratios, and assessed the relationship of CB:PB and postmortem interval for THC and THCCOOH. Correlations of preserved compared to unpreserved blood were strong with r2 > 0.97. The median CB:PB ratios were 1.1 and 1.3 for THC and THCCOOH, respectively. THCCOOH CB:PB was significantly higher than 1.0 (p-value < 0.001). The CB:PB ratio was only weakly correlated with PMI for both compounds. The median blood-to-”serum” ratio was 1.0 for THC and 0.8 for THCCOOH. The blood-to-”serum” ratio of THCCOOH was significantly lower than 1.0 (p-value < 0.001). Results demonstrated minimal potential for postmortem redistribution of THC and THCCOOH and that the ratio of blood-to-”serum” in postmortem samples differs from the blood-to-plasma ratio established in living humans. Based on these results, it is not recommended to apply a correction factor to THC and THCCOOH concentrations from postmortem blood samples. Our study improves the understanding of postmortem cannabinoid concentrations to support forensic interpretation in cases of fatal motor vehicle accidents.