Occasionally, obtaining an adequate or acceptable postmortem blood specimen for drug analysis is not possible due to factors, such as decomposition, exsanguination, or embalming. Submandibular salivary gland tissue, one of three major types of salivary gland tissue in the oral cavity of humans, has been reported to be a viable alternative postmortem specimen for toxicological testing. In this study, we evaluated the performance of the Randox Evidence Investigator instrument and Randox DOA (Drugs of Abuse) Ultra Whole Blood Array for the semi-quantitative determination of 21 immunoassays in an alternative matrix, submandibular salivary gland tissue. We analyzed 132 submandibular salivary gland tissue specimens and compared the generated results to concomitantly collected postmortem whole blood specimen results. Oxycodone 2, meprobamate, barbiturate, benzodiazepine assay 1, zolpidem, and buprenorphine all showed perfect agreement (Cohen's kappa score = 1.00) between the submandibular salivary gland tissue results and the postmortem whole blood results; dextromethorphan, fentanyl, benzoylecgonine, methamphetamine, tricyclic antidepressants, oxycodone 1, and opiate showed an almost perfect agreement (Cohen's kappa score = 0.81-0.99); methadone, generic opioids, and amphetamine exhibited substantial agreement (Cohen's kappa score = 0.61-0.80). Tramadol demonstrated fair agreement (Cohen's kappa score = 0.41-0.60). The lowest measure of agreement was observed with cannabinoids, meeting criteria for slight agreement (Cohen's kappa score = 0.01-0.20). An application of the techniques described in this study could be implemented in postmortem toxicology laboratories as well as medical examiners offices to provide preliminary drugs of abuse test results that can be used to direct additional testing. This study highlights the successful integration of a novel specimen matrix and an "off-label" use of an established analytical technique.
