| Summary: | Abstract Background This study examines trends in delta-9-tetrahydrocannabinol-9-carboxylic acid (THC-COOH) positivity rates in pre-employment urine drug screenings at a single university-based hospital occupational medicine clinic from 2017 to 2022, following California’s recreational cannabis legalization in 2016, with sales beginning officially on January 1, 2018. Methods Retrospective analysis of 21,546 de-identified urine drug screenings from 2017 to 2022 was conducted. Initial screening used instant urine drug immunoassays (50 ng/mL cutoff for THC-COOH), followed by confirmatory gas chromatography-mass spectrometry (15 ng/mL cutoff). Positivity rates were calculated annually, and descriptive statistics summarized age and gender distributions among positive cases. The Cochran-Armitage trend test assessed temporal trends. Results Of 21,546 screenings, 92 (0.44%) were THC-COOH-positive. The positivity rate increased from 0.12% (4/3,215) in 2017 to 0.94% (45/4,784) in 2022 (Cochran-Armitage, Z = 5.19, p < 0.001), a 683.33% relative increase (absolute change: 0.82%). Among positive cases, 76% were aged 20–39 (mean: 29.00 years, SD = 9.5), and the female proportion rose from 25.00 to 62.22%. Median THC-COOH levels ranged from 60.00 to 176.50 ng/mL (overall: 145.0, IQR: 309.5). Conclusion THC-COOH positivity rates increased significantly post-legalization, potentially influenced by increased cannabis use. Urine tests detect past use, not impairment, highlighting the need for impairment-focused testing per Assembly Bill 2188 (2024). Missing total sample demographic data limit age/gender subgroup analyses.
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