Comparison of Drug Concentrations in Blood and Oral Fluid Collected with the Intercept® Sampling Device

The aim of the study was to determine drug concentration ratios between oral fluid collected with the Intercept device and whole blood. Samples of blood and oral fluid were obtained from patients admitted to acute psychiatric treatment and drivers suspected of drugged driving. Samples were analyzed for illegal drugs, benzodiazepines, opioids, carisoprodol, and meprobamate. Drugs were detected in samples of both blood and oral fluid from 59 subjects; altogether, 17 different drugs were found. Concentration ratios between oral fluid and blood were determined for all cases. The distributions of drug concentration ratios were wide for most drugs and do not allow reliable estimations of drug concentrations in blood using concentrations in oral fluid. The median oral fluid/blood drug concentration ratios for the most prevalent drugs were 0.036 diazepam, 0.027 nordiazepam, 7.1 amphetamine, 2.9 methamphetamine, 5.4 codeine, 1.9 morphine, and 4.7 tetrahydrocannabinol. The correlation coefficients between drug concentrations in oral fluid and blood ranged from 0.15 to 0.96 for the six most prevalent drugs.