Stability of 9-Tetrahydrocannabinol (THC), 11-Hydroxy-THC, and 11-Nor-9-carboxy-THC in Blood and Plasma

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Abstract
The stabilities of Δ9-tetrahydrocannabinol (THC) end two of its metabolites, 11-hydroxy-Δ9-tetrahydrocannabinol (HO-THC) and 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (COOH-THC), were determined in blood and plasma stored at −10°C, 4°C, and room temperature. Each of the cannabinoids was added to freshly-drawn blood and plasma to give concentrations of 20 ng/mL. Two-mL allquots were stored in silanized tubes and the cannabinoid concentrations were monitored by gas chromatography/mass spectrometry over a 6-month period. No significant changes were observed in the concentrations of the cannabinoids for the first month of storage. However, the concentrations of THC and HO-THC in blood stored at room temperature had decreased significantly at 2 months. No statistically significant changes were detected in cannabinoid concentrations in plasma or blood stored at 4° or −10°C for up to 4 months. After 6 months at room temperature, the blood concentrations of THC and HO-THC had decreased by 90 and 44%, respectively, whereas the concentration of COOH-THC was not significantly different from the control. The possibility of loss of cannabinoids from blood due to adsorption onto the grey stoppers used in Venoject® tubes was also investigated. Over a 24-hr period, no significant differences were detected in any of the cannabinoid concentrations regardless of sample size (1.3 or 8 mL), differences in temperature (−10°C, 4°C, or room temperature), or extent of contact with the tube's stoppers.

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