This secondary analysis sought to determine the agreement between a trauma patient’s self-reported drug use and biochemical drug testing via urine tox screen. These findings suggest that in patients with traumatic injury, self-report is a valid proxy for ruling out drug use, and there were no apparent differences in the validity of using self-report for cannabis compared to other drugs.

There are several advantages to being able to rely on self-reported drug use, such as immediate results, no cost, and noninvasiveness. Self-report is also incentivized by hospitals because insurance companies in some states are allowed to deny reimbursement if an injury resulted from alcohol and drug use (Elkbuli et al. 2019).

However, there are clinical concerns with undisclosed drug use for patients presenting acutely to the ED. Drug use can confound vital sign assessments, diagnosis, and treatment (DiGiorgio et al. 2020), there are implications for drug-drug interactions (Dydyk et al. 2020), and risk for withdrawal (Arroyo-Novoa et al. 2020; Jawa et al. 2014; Salottolo et al. 2017), and there are negative effects on acute pain management (Salottolo et al. 2019; Salottolo et al. 2018) and clinical outcomes (Taghavi et al. 2021). Because of these concerns with undisclosed drug use, there is frequent debate about biochemically testing trauma patients for drugs. Our experience suggests clinicians are hesitant to rely on self-report, instead requesting a tox screen to determine if drugs are present. Tox screens were performed in 59% of trauma patients in this study, in the range reported in the literature of 36% (London and Battistella 2007) to 85% (Grigorian et al. 2019).

While these findings suggest there is utility in using self-reported drug use in trauma patients, as undisclosed use was rare for cannabis and other drugs, the implications of our findings should be considered with the study size and setting. Only 190 of 320 trauma patients had biochemical drug testing, and most of our population was admitted to hospitals in Colorado, the first state to legalize and commercialize cannabis. Patients in Colorado may be more willing to divulge drug use, especially cannabis. Currently, 37 states plus the District of Columbia, Guam, and the US Virgin Islands have permissive cannabis laws legalizing medical cannabis (National Conference of State Legislatures 2021), but our findings may not be generalizable to states with strict marijuana laws where medical and recreational cannabis are illegal. Published studies demonstrate an increase in self-reported cannabis use after medical legalization (Levine et al. 2021) and recreational legalization (Grigorian et al. 2019; Jennings et al. 2019), although one study reported a decrease in the percent of patients self-reporting use after medical marijuana legalization (Claudius et al. 2020).

Vitale et al. recommend using drug self-report in patients presenting to the ED for injuries or illness because it provides more accurate information than the ‘gold standard’ of biochemical testing for both alcohol and drugs (Vitale et al. 2006). In our study, sensitivity and positive predictive values were poor, suggesting that a negative tox screen may not accurately recognize a patient who is a current drug user. The sensitivity of cannabis was 60% in our study. Similarly, Claudius et al. reported 53% of trauma patients testing positive for cannabis also self-reported use (Claudius et al. 2020). In a roadside survey in Belgium, self-reported cannabis use was compared with biochemical testing in nearly 3000 drivers; there was high specificity (94–99%) but low sensitivity (22–58%) between self-report and biochemical testing (Van der Linden et al. 2014).

This study has limitations. Primarily, tox screens are not routinely ordered on all trauma patients or on a random set of patients. Results would be more interpretable in a setting with universal biochemical testing. Tox screens are typically ordered in the trauma setting based on clinical relevance (e.g., differential diagnosis or in treatment) and injury characteristics (e.g., severity, cause, or mechanism). In some settings, tox screens are ordered on clinical suspicion or to confirm drug usage. In our study, the proportion of patients who had a tox screen were statistically identical by self-reported drug use vs. non-use (60% vs. 59%). Demographic characteristics were also similar based on whether a tox screen was done. There were differences based on cause of injury: tox screens were more frequently ordered for patients with a MVC injury. Had there been differences in tox screen testing based on self-reported drug use or demographics, this would have been a major source of selection bias. Fortunately, this was not observed. Still, future studies should test all patients or a random sample of patients in order to confirm our findings. A related limitation is that the statistical analyses were limited to the 59% of patients who had a tox screen. Based on prior studies at U.S. trauma centers, biochemical testing is ordered for 36 to 85% of trauma admissions, similar to what we are reporting.

Additional limitations are as follows. Third, this was a post hoc analysis of two convenience samples, and the populations differed in age, ISS, and cause of injury. Fourth, patients who were aware their urine was being collected for biochemical testing may have also been more willing to divulge illicit drug use, despite the risk of retribution or penalty. However, our data do not support this possibility since self-reported drug use was reported in 23.1% without a tox screen and 23.7% who had a tox screen (p = 0.90). Fifth, patients who were immediately treated with opiates or other benzodiazepines may have been misclassified as a positive tox screen, because urine sample collection is generally performed on admission and not in the ED. Finally, it is possible that the tox screen was negative because the drug was not present in detectable concentrations at the time of hospital admission. Approximate drug detection times in urine vary based on drug (Moeller et al. 2017). Alternatively, synthetic “designer” drugs, which are increasingly used, although still rare at only 1.2% of teens and young adults (Palamar et al. 2015), may be undetected in routine urine tox screens (Luethi and Liechti 2020).