The utility of visual appearance in predicting the composition of street opioids

Abstract

Background: With the emergence of unregulated fentanyl, people who use unregulated opioids are increasingly relying on appearance in an effort to ascertain the presence of fentanyl and level of drug potency. However, the utility of visual inspection to identify drug composition in the fentanyl era has not been assessed. Methods: We assessed client expectation, appearance, and composition of street drug samples being presented for drug checking. Results of a visual screening test were compared to fentanyl immunoassay strip testing. We calculated sensitivity, specificity and likelihood ratios (LR) to assess the accuracy of the common assumption that samples with a “pebbles” appearance contain fentanyl. Results: In total, of the 2502 unregulated opioid samples tested, 1820 (73.5%) appeared as “pebbles”, of which 1729 (95.0%) tested positive for fentanyl for a sensitivity of 75.9% (95% Confidence Interval [CI]: 74.2–77.6) and specificity of 59.4% (95%CI: 57.5–61.3). Although, the odds of samples containing fentanyl was 4.60 (95%CI: 3.47−6.11) times higher among pebbles samples compared to non-pebble samples, the positive LR for pebbles to contain fentanyl was only 1.87 (CI: 1.59–2.19). The negative LR was more useful at 0.41 (95% CI: 0.36−0.46). Conclusions: A positive screening test for pebbles is not strongly enough associated to be used as a proxy for detecting fentanyl. While the absence of the appearance of pebbles does somewhat reduce the likelihood of fentanyl being present in a given sample, the high prevalence of fentanyl and fentanyl analogues in the drug supply and the risks of consumption are such that public health providers should routinely advise people who use unregulated opioids against solely relying on visual characteristics of drugs as a harm reduction strategy.

Keywords:

• Drug checking
• opioids
• fentanyl
• harm reduction
• overdose

Acknowledgments

The authors would like to express our sincere thanks to current and past researchers and staff. The authors would also like to thank the staff at Portland Hotel Society, Lookout Housing and Health Society, Vancouver Coastal Health, and Fraser Health for their collaboration in implementing drug checking services at the sites where this study was conducted, and to all study participants. This research was undertaken, in part, thanks to funding from the Canada Research Chairs program through a Tier 1 Canada Research Chair in Addiction Medicine which supports EW. LT is supported by a Michael Smith Foundation for Health Research (MSFHR) Scholar Award. Funding agencies had no role in the research, design, or writing of the manuscript, nor did they have a role in the decision to submit the paper for publication. No financial disclosures were reported by the authors of this paper.

Disclosure statement

This research was undertaken, in part, thanks to funding from the Canada Research Chairs program through a Tier 1 Canada Research Chair in Addiction Medicine which supports EW. LT is supported by a Michael Smith Foundation for Health Research (MSFHR) Scholar Award. Funding agencies had no role in the research, design, or writing of the manuscript, nor did they have a role in the decision to submit the paper for publication. No authors have financial disclosures to make. No financial disclosures were reported by the authors of this paper.

Author contributions

KM, LT, ML, and EW were responsible for the study design; LT conducted the statistical analyses; KM prepared the first draft of the manuscript; all authors provided critical comments on the first draft of the manuscript and approved the final version to be submitted.

Additional information

Funding

The study was supported by a Health Canada Substance Use and Addictions Program grant to the BC Center on Substance Use to implement and evaluate a drug checking pilot in British Columbia. [Arrangement #: 1718-HQ-000024].