Effect of Blood Collection Time on Measured Δ9-Tetrahydrocannabinol Concentrations: Implications for Driving Interpretation and Drug Policy. (6th January 2020)

• Record Type: Journal Article
• Authors: Hartman, Rebecca L; Brown, Timothy L; Milavetz, Gary; Spurgin, Andrew; Gorelick, David A; Gaffney, Gary R; Huestis, Marilyn A
• Is Part Of: Clinical chemistry. Volume 62:Number 2(2016)
• Page Start: 367
• Page End: 377
• Publication Date: 2020-01-06
• Subjects: Clinical chemistry -- Periodicals; Pharmaceutical chemistry -- Periodicals; Biochemistry -- Periodicals; Biochimie -- Périodiques; Diagnostics biologiques -- Périodiques; Biochemistry; Clinical chemistry; Pharmaceutical chemistry; Biochemistry; Laboratory Techniques and Procedures; Klinische chemie; Periodicals; 616.075605
• DOI: 10.1373/clinchem.2015.248492
• Languages: English
• ISSNs: 0009-9147

Abstract

Abstract: BACKGROUND: In driving-under-the-influence cases, blood typically is collected approximately 1.5–4 h after an incident, with unknown last intake time. This complicates blood Δ 9 -tetrahydrocannabinol (THC) interpretation, owing to rapidly decreasing concentrations immediately after inhalation. We evaluated how decreases in blood THC concentration before collection may affect interpretation of toxicological results. METHODS: Adult cannabis smokers (≥1×/3 months, ≤3 days/week) drank placebo or low-dose alcohol (approximately 0.065% peak breath alcohol concentration) 10 min before inhaling 500 mg placebo, 2.9%, or 6.7% vaporized THC (within-individuals), then took simulated drives 0.5–1.3 h postdose. Blood THC concentrations were determined before and up to 8.3 h postdose (limit of quantification 1 μg/L). RESULTS: In 18 participants, observed Cmax (at 0.17 h) for active (2.9 or 6.7% THC) cannabis were [median (range)] 38.2 μg/L (11.4–137) without alcohol and 47.9 μg/L (13.0–210) with alcohol. THC Cmax concentration decreased 73.5% (3.3%–89.5%) without alcohol and 75.1% (11.5%–85.4%) with alcohol in the first half-hour after active cannabis and 90.3% (76.1%–100%) and 91.3% (53.8%–97.0%), respectively, by 1.4 h postdose. When residual THC (from previous self-administration) was present, concentrations rapidly decreased to preinhalation baselines and fluctuated around them. During-drive THC concentrations previously associated with impairment (≥8.2 μg/L) decreased to median <5 μg/L by 3.3 h postdose and <2 μg/L by 4.8 h postdose; only 1 participant had THC ≥5 μg/L after 3.3 h. CONCLUSIONS: Forensic blood THC concentrations may be lower than common per se cutoffs despite greatly exceeding them while driving. Concentrations during driving cannot be back-extrapolated because of unknown time after intake and interindividual variability in rates of decrease.