Stability of delta 9-tetrahydrocannabinol (THC), 11-hydroxy-THC, and 11-nor-9-carboxy-THC in blood and plasma.

The stabilities of delta 9-tetrahydrocannabinol (THC) and two of its metabolites, 11-hydroxy-delta 9-tetrahydrocannabinol (HO-THC) and 11-nor-9-carboxy-delta 9-tetrahydrocannabinol (COOH-THC), were determined in blood and plasma stored at -10 degrees C, 4 degrees 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 aliquots 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 degrees or -10 degrees 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 degrees C, 4 degrees C, or room temperature), or extent of contact with the tube's stoppers.