Muscle can provide evidence of cannabinoids when blood is unavailable, but a muscle concentration is not an interchangeable blood concentration. Pettersen and colleagues’ 39-case autopsy study found THC and CBD in psoas and vastus lateralis muscle, with wide variation between muscle and femoral-blood results. The findings support alternative-specimen detection more strongly than a fixed conversion.
Which cases and specimens were included?
The study selected 39 cases from a larger autopsy project after routine blood testing detected THC. Specimens were collected in parallel at Oslo medicolegal autopsies during 2013–2016. The postmortem interval ranged from zero to six days. Thirty-six cases had no or slight decomposition, one had moderate decomposition and two were ungraded. Extensive burns, severe putrefaction and major blood loss were not represented as the study’s target conditions.
Peripheral blood came from the femoral vein. Blood and muscle were placed in polypropylene tubes containing potassium fluoride. Specimens were refrigerated at 4°C until analysis, generally within one to two weeks. Muscle was homogenized with water before extraction, and reported concentrations were corrected for that preparation dilution.
The anatomical muscle site mattered
THC was detected in 36 psoas specimens and 36 vastus lateralis specimens. CBD was detected in 35 psoas specimens and 33 vastus lateralis specimens, compared with 35 CBD-positive peripheral-blood specimens among the 39 THC-selected cases.
The median muscle-to-blood ratios for THC were 2.2 for psoas, ranging 0.11–17, and 5.5 for vastus lateralis, ranging 0.14–29. For CBD, corresponding medians were 2.2 and 4.2, with ranges 0.037–18 and 0.036–32. Because muscle was reported in mg/kg and blood in mg/L, these quotient values carry dimensions of L/kg; they are not dimensionless comparisons of identical materials.
Removing four vastus-lateralis THC outliers changed its median ratio from 5.5 to 4.0 and narrowed the range. That sensitivity reinforces why a published median should not be treated as a dependable divisor for an individual specimen.
Correlation did not establish interchangeability
Spearman correlations with peripheral blood were 0.57 for psoas THC and 0.45 for vastus-lateralis THC; CBD correlations were 0.64 and 0.35, respectively. These associations were statistically significant, but significance does not eliminate the wide individual ratios or validate a blood-prediction equation.
The authors found no systematic ratio differences with postmortem interval. That observation does not prove absence of redistribution. Samples were collected at one postmortem time point, and no antemortem specimens were available.
Screening and confirmation were separate
Routine peripheral-blood THC testing used UHPLC–MS/MS. Subsequent confirmation and quantitation of THC and CBD across the project specimens used GC–MS with selected-ion monitoring. The reported quantification limit was 0.0002 mg/L for both analytes. The reported long-term bias and precision data came from whole-blood controls, so they should not be represented as a complete independent muscle-validation package.
Whole-blood between-day CVs were 9% for both analytes at 0.0008 mg/L; at 0.0032 mg/L they were 9% for THC and 5% for CBD. Homogenization and matrix-specific performance remain important when evaluating an actual muscle result.
A useful alternative with a narrower inference
A confirmed muscle finding may support cannabinoid detection. This study did not establish an administered dose, time of use, impairment or cause of death from muscle concentration. Its selected, largely minimally decomposed cases also do not validate performance in every badly damaged body.
The same distinction between useful detection and quantitative substitution appears in vitreous drug screening. The appropriate matrix must be considered for the specific analyte and analytical method.
Primary source
Pettersen S, Øiestad ÅML, Rogde S, Brochmann GW, Øiestad EL, Vindenes V. Distribution of tetrahydrocannabinol and cannabidiol in several different postmortem matrices. Forensic Science International. 2021;329:111082. doi:10.1016/j.forsciint.2021.111082.
Leave a Reply