Assessment of postmortem urine fentanyl detection by autopsy dipstick testing in accidental overdose deaths

Accidental overdose cases continue to rise due to the opioid epidemic in the USA, namely, the widespread availability and use of fentanyl. Medical examiners and coroners across the country have been subsequently burdened, and with limited resources, some seek alternative triaging processes to identify overdoses. Point-of-care urine dipstick testing at autopsy is one such idea that may be used in various ways to instigate or negate the need for an autopsy or regular forensic toxicology laboratory testing. This study investigated the frequency and estimated quantitative fentanyl and norfentanyl concentrations in the postmortem urine of fentanyl-related accidental overdose deaths, as well as the effectiveness of commercially available point-of-care urine dipstick tests based on such concentrations. A total of 1550 fentanyl-related accidental overdose cases, where both the postmortem peripheral femoral blood and urine were tested, were reviewed. Of these, using sensitive liquid chromatography-tandem mass spectrometry (LC-MS-MS) laboratory testing, 82 cases (5%) had a positive fentanyl or norfentanyl detection in the blood, while fentanyl or norfentanyl remained undetected in the urine. Furthermore, a comparison of commercially available urine dipstick test cut-offs and authentic casework with estimated urine concentrations revealed that at a fentanyl/norfentanyl cut-off level of 5 ng/mL, 19% of these fentanyl-related accidental overdoses would result in a false negative, 24% at 10 ng/mL, 25% at 20 ng/mL, 51% at 50 ng/mL, and 61% at 100 ng/mL. The study found that the use of urine dipstick tests, as a decision-maker for the initiation of further comprehensive routine toxicology laboratory testing, or to support cause and manner of death determination, leads to both false-positive and false-negative predictions in fentanyl accidental overdoses.