Drug Use during Incarceration: A Comprehensive Quality and Prevalence Study in Three Danish Prisons

Drug use in Danish prisons has previously not been investigated in detail using confirmatory, laboratory analysis. The objective of the present quality study, initiated by the Danish Prison and Probation Service, was to i) evaluate the performance of an initial, on-site drug screening strategy; ii) gain insights into emerging drug trends; and iii) suggest evidence-based strategies for future drug testing.

Over a two-year period, routine urine samples (n = 1952 from 710 inmates) from three Danish prisons were subjected to comprehensive drug testing. Immunoassay screening was conducted on-site. A parallel sample aliquot was forwarded to laboratory analysis by confirmatory methods: High-performance liquid chromatography and tandem mass spectrometry (LC-MS/MS) and gas chromatography and mass spectrometry (GC-MS) targeting 56 drugs-of-abuse/medical drugs, 26 key metabolites, 41 new psychoactive substances (NPS), including specific biomarkers for heroin, crack cocaine, or ethanol (a total of 123 target analytes/sample).

The on-site immunoassay method showed a sensitivity from 66 to 100%; specificity was above 98%; accuracy was above 95%. Laboratory analysis detected compounds not screened for including tramadol, oxycodone, buprenorphine, ketamine, MDMA, 4-fluoroamphetamine, and GHB. The prevalence of drug use was in the order: cannabis > ethanol > cocaine > benzodiazepines > amphetamine.

The performance of the immunoassay was found acceptable; however, the screening program was inadequate for detecting other significant substances. Based on these findings, a broader screening method will be implemented in future at Danish Prisons to minimize false negative results. The data did not indicate a trend of using NPS in Danish prisons.