Under-Reporting of Drug Use in Douliu, Taiwan: Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) Screening Identifies Cases Beyond Education and Tattoo Markers in an Emergency Department Cohort.

Background: Substance abuse drives considerable emergency department (ED) demand and remains a major public-health issue. Although low educational attainment and tattoos are linked to high-risk behaviors, their relevance to drug-positive ED visits in Taiwan is unknown. Self-reported drug histories are also unreliable, with many patients denying use despite positive toxicology. We therefore examined these sociocultural markers in confirmed drug-positive cases to assess their value for ED risk stratification. Methods: This single-center descriptive cohort of ED patients with urine-confirmed illicit drug positivity summarized demographic/social characteristics, toxicology findings, and clinical presentations, with prespecified within-cohort contrasts (Fisher's exact and Mann-Whitney U; two-sided α = 0.05) across traffic injury, self-harm, and other presentations; no drug-negative control group was enrolled. Results: The cohort was predominantly male (83.3%) with a median age of 39 years (range, 17-74). Lower educational attainment (≤ upper secondary [senior/vocational high school; ISCED 0-3]) was observed in 40/54 (74.1%; 95% CI, 61.1-83.9), and visible tattoos in 32/54 (59.3%; 95% CI, 46.0-71.3) among drug-positive ED patients. Overall, 92.6% (95% CI, 82.4-97.1) of toxicology-confirmed drug-positive patients denied recent drug use, indicating approximately 13-fold under-detection by history alone. Methamphetamine was the leading substance (42.6%), and 85.0% had ≥ 2 psychoactive substances detected. These estimates are descriptive of the drug-positive cohort; no drug-negative comparator was enrolled. Conclusion: In this mixed urban-rural ED cohort with toxicology-confirmed illicit drug use, lower educational attainment and tattoo presence were commonly observed. Because the study lacked a drug-negative control group, these findings should be interpreted as descriptive rather than evidence of association. The very high prevalence of under-reporting indicates that history alone has limited sensitivity for detecting recent drug use and supports a low threshold for comprehensive toxicology testing, particularly in high-risk presentations and injured drivers. Methamphetamine predominance, frequent polysubstance exposure, and approximately one-in-five drug-positive presentations following traffic injuries highlight the need for clinical vigilance. These descriptive patterns warrant evaluation in multicenter prospective studies with quantitative toxicology capable of assessing impairment and causal relationships.