Postmortem Clinical Testing

Oral Cavity Fluid as an Alternative Postmortem Matrix

“…9,29 Analytes that are more basic in nature (higher pK a ) tend to partition to and become trapped in oral fluid. 25,30 The passive diffusion of drugs or metabolites from blood to oral fluid is influenced greatly by 5 factors: the analytes pK a , protein binding, lipophilicity, spatial configuration, and molecular size. 25,[30][31][32] Free unbound drugs make their way into the oral cavity through passive diffusion, and once in the oral cavity, they remain there because of ion trapping.…”

“…25,30 The passive diffusion of drugs or metabolites from blood to oral fluid is influenced greatly by 5 factors: the analytes pK a , protein binding, lipophilicity, spatial configuration, and molecular size. 25,[30][31][32] Free unbound drugs make their way into the oral cavity through passive diffusion, and once in the oral cavity, they remain there because of ion trapping. Ion trapping occurs because of the difference in the pH of OCF and the pH of blood.…”

“…Ion trapping occurs because of the difference in the pH of OCF and the pH of blood. [30][31][32] Only free and unionized drugs make their way into oral fluid, and that is why there is a correlation to blood plasma concentrations. 25,[30][31][32] Of the 62 paired samples analyzed, analytes were found in the OCF of 56 cases (90%), with 3 of these cases not having any analytes detected in the blood or urine.…”

“…[30][31][32] Only free and unionized drugs make their way into oral fluid, and that is why there is a correlation to blood plasma concentrations. 25,[30][31][32] Of the 62 paired samples analyzed, analytes were found in the OCF of 56 cases (90%), with 3 of these cases not having any analytes detected in the blood or urine. In one case where no drugs or metabolites were detected in the OCF and blood (case 48), urine had positive results for morphine, oxymorphone, and THC with codeine and oxycodone in low concentrations (Supplemental Table 1, http://links.lww.com/ FMP/A62).…”

“…25 Unlike the antemortem study, 25 alprazolam (n = 10) detection in OCF outperformed blood with a 100% detection rate, with zero cases that detected alprazolam in urine or blood without a detection in OCF. Antemortem oral fluid concentrations are often considered comparable to blood concentrations with multiple studies in blood and oral fluid concentrations, 19,20,25,30,31,37,38 including studies with simultaneous collection of oral fluid and blood for comparison of results. 19,20,25,38 Studies with paired samples are crucial for comparison of these matrices, and to the knowledge of the authors, this study is the most extensive comparison of paired postmortem OCF samples with blood, urine, vitreous fluid, and bladder wash in some instances.…”