Comment on Chang et al.: defining the added interpretive value of brain fentanyl testing at low blood concentrations.

Chang et al. report substantial variability in fentanyl blood-to-brain relationships and suggest that brain testing may be beneficial in suspected overdose cases with low peripheral blood concentrations. We suggest that this implication would be strengthened by distinguishing analytical confirmation from incremental forensic interpretation. Demonstrating fentanyl in a second matrix does not itself establish that the brain result changes attribution of fentanyl's role in death. A focused analysis of low-blood cases in which brain findings altered interpretation, supported by scene, autopsy, and co-intoxicant data, would better define the practical value of brain testing.