Urinary Excretion Profiles of 11-Nor-9-Carboxy-delta9-Tetrahydrocannabinol: A delta9-THCCOOH to Creatinine Ratio Study

Published: Journal of Analytical Toxicology, Volume 23, Number 6, October 1999, pp.531-534

Urinary Excretion Profiles of 11-Nor-9-Carboxy-D9-Tetrahydrocannabinol: A D9-THCCOOH to Creatinine Ratio Study
Albert D. Fraser and David Worth

Monitoring the major cannabinoid metabolite (D9-THCCOOH) to creatinine ratio (M/C) has been used to predict new drug use. According to Huestis and Cone, the best accuracy (85.4%) for predicting new marijuana use was a ratio ³ 0.5 from two urine specimens collected at least 24 h apart. Manno et al. recommended an M/C ratio of ³ 1.5. Subjects with a history of chronic marijuana use were screened for cannabinoid use by immunoassay (50-ng/mL cutoff), and presumptive positives were confirmed by gas chromatography–mass spectrometry for D9-THCCOOH (15-ng/mL cutoff). Creatinine was analyzed with a cutoff concentration of 25 mg/dL. The study objective was to apply the criteria from both groups of workers to determine if consecutive urine specimens (collected at least 24 h apart) positive for cannabinoids could be used to differentiate new marijuana use from the excretion of residual cannabinoid metabolite (D9-THCCOOH) in an uncontrolled setting. Serial urine specimens (826) were collected from 26 individuals. Huestis and Cone and Manno et al. ratios indicated new drug use in 83% and 33% of serial urine specimens collected at least 24 h apart, respectively. Clinically, the Huestis and Cone ratio is recommended because of a lower false-negative rate (7.4%) than the Manno et al. false-negative rate (24%). In legal situations, we recommend using the Manno et al. ratio because of its lower false-positive rate (0.1%) as stated by Huestis and Cone.

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