Non-prescription Fentanyl Positive Toxicology: Prevalence, Positive Predictive Value of Fentanyl Immunoassay Screening, and Description of Co-substance Use

Abstract

Objectives: Opioid overdose deaths in Massachusetts linked to illicitly-manufactured fentanyl have increased dramatically. In response, an urban safety-net hospital added urine fentanyl testing with reflex confirmation testing to its standard urine toxicology panel. The goals of this study were to describe fentanyl toxicology test results, identify the positive predictive value of presumptive fentanyl immunoassay, and describe co-substance use among those with unexpected fentanyl positive results. Methods: We included urine toxicology tests from January through June 2016 analyzed at an urban safety-net hospital. We excluded tests from individuals prescribed or administered fentanyl within the preceding 72 hours. Positive fentanyl immunoassay tests underwent reflex chromatography confirmation testing. Samples that confirmed positive for acetyl fentanyl and/or fentanyl and/or norfentanyl were considered true positives. Results: Of 11,873 urine samples, 10.4% of samples screened fentanyl positive and 8.8% were confirmed fentanyl positive. The positive predictive value of a positive urine fentanyl screen was 85.7%. Of 4398 unique patients, 13.2% had at least 1 test confirmed positive for nonprescription fentanyl. Patients with a confirmed fentanyl positive drug test were more likely to have positive urine drug test for barbiturates, benzodiazepines, cocaine, methadone, and opiates, and less likely to have oxycodone or buprenorphine. Conclusions: At an urban safety-net hospital, nonprescription fentanyl use was common and was associated with greater use of other substances favoring routine fentanyl testing. Although the positive predictive value of the screening test was high, confirmation testing detected substantial numbers of false positives, especially in older patients. Therefore, fentanyl confirmation testing should be used when results will change treatment approach and patient education.

Evaluation of “Real-Time” Fatal Drug Overdose Surveillance by King County Medical Examiner's Office, Seattle, Washington

“…Guidelines for certification of overdose deaths published by the National Association of Medical Examiners 25 recommend against using screening methods to certify deaths because of the inherent false-positive rates of these tests. 26,27 While this study certainly supports this recommendation, the results also indicate that RDC can be achieved in many cases by the RDC methodology described herein, adhering to a strict protocol relying on concurrence of information gathered from scene investigation, autopsy findings, screening autopsy blood and urine, and testing drug evidence collected from scenes. Over the 3-year period KCMEO certified 56% of 1797 overdose deaths within 1 to 3 days.…”

Fentanyl Exposure and Detection Strategies Utilized by Clinical Trial Participants Seeking Linkage to Opioid Use Disorder Treatment at a Syringe Service Program

“…While fentanyl has a short half-life (3–12 h) and only a small amount is secreted in urine, the manufacturer of the test used in this study states it is reactive to fentanyl’s metabolite norfentanyl for a maximum 3-day urine detection window. Finally, it is possible that polysubstance use and the possible presence of other adulterating substances (such as nitazines and xylazine) could have affected urine test results through cross-reactivity or metabolic interactions [ 49 – 51 ].…”

Evaluation of in‐house drug evidence testing by King County Medical Examiner's Office in “real‐time” fatal overdose surveillance

“…In response to the ever‐expanding drug overdose epidemic [1–7], medical examiners and coroners, public health agencies, and toxicology laboratories have initiated a variety of surveillance efforts to monitor the progression of the crisis with respect to overdose fatalities and the appearance of novel drugs appearing in communities across the US [8–28]. In 2018, the King County Medical Examiner's Office (KCMEO), a division of Public Health – Seattle and King County, in Seattle, Washington, initiated a “real‐time” surveillance project using toxicology screening methods for in‐house testing of decedents' blood and urine samples.…”