Fentanyl concentrations for peripheral blood and brain samples in non-medical postmortem cases

Fentanyl prevalence has increased exponentially in all forensic toxicology case types since the start of the current epidemic in 2016. Prior to 2016, fentanyl detected in postmortem cases was typically seen from use or misuse of medicinal administration. However, with the current epidemic, fentanyl use is from the illicit drug market and concentrations are substantially higher complicating interpretation. Additionally, factors contributing to postmortem redistribution of fentanyl can play a large role in interpretation. In combination with peripheral blood (PPH), brain concentrations can aid interpretation due to the isolated and protected location of the brain. A total of 566 cases were evaluated, and after excluding four outliers, the 562 cases had an overall fentanyl PPH mean of 18 ng/mL, median of 10 ng/mL, and range of 0.53-555 ng/mL. Overall mean, median, and range of fentanyl concentrations in brain samples were 61 ng/g, 34 ng/g, and 0.73-3100 ng/g, respectively. Three concentration ranges, low (≤10 ng/mL), medium (>10-50 ng/mL) and high (> 50 ng/mL), derived from PPH were established to evaluate cases based off various concentrations. The median blood-to-brain ratio doubled between the low and high bins. There was a greater percentage of females in the high concentration bin as compared to the low and medium bins. The younger age group from 15 to 24 years old showed a higher prevalence of fentanyl in the medium group rather than the others. The blood:brain ratio for all cases had a mean of 0.36, a median of 0.29, and a range of 0.03 to 2.57. The wide range of blood:brain ratios indicated that using singular information to interpret the case can be misleading. However, it does show the benefits of testing brain samples in suspected overdose cases where the fentanyl blood concentrations are low.