Identification of controlled and non‐controlled substances by forensic laboratories: Results from a 2023 interlaboratory study

Forensic laboratories analyze seized drug evidence using analytical schemes designed to ensure reliable identification results; however, there is little empirical evidence on how these schemes perform when applied to complex samples and how reporting practices influence results. This Interlaboratory Study (ILS) evaluated identification accuracy and reporting practices of forensic laboratories when analyzing samples containing mixtures of controlled and non-controlled substances. Eighty-one laboratories analyzed mock casework samples reflecting the complexity of seized drug evidence. Laboratories used their routine analytical schemes, which were evaluated for ASTM E2329-17 compliance. Results were classified by compound, reporting category, and reported identification rate (RIR). Overall, 99% of reported identification results were ASTM E2329-17 compliant. Federally controlled compounds were identified and reported with high RIRs (>0.85) for Full Identifications. Positional isomers or non-controlled substances were frequently underreported or reported as Partial Identifications. In this study, underreporting refers to instances in which a compound was detected or partially identified experimentally but not specifically reported in the final laboratory report, including instances where positional isomers were not distinguished and a generalized identification (e.g., class-level or non-specific designation) was reported instead. Incorrect identifications were rare (<2%) and were primarily due to incorrect positional isomer reporting. Reporting outcomes were strongly influenced by laboratory policies, statutory requirements, an availability of reference material, rather than analytical capability alone. Results from this ILS highlight complex factors that can result in underreporting of compounds and the implications when data from forensic laboratories are used for public health surveillance and policy development.