In vitro stability of free and glucuronidated cannabinoids in blood and plasma following controlled smoked cannabis.

Background: Blood and plasma cannabinoid stability is important for test interpretation and is best studied in authentic rather than fortified samples.
Methods: Low and high blood and plasma pools were created for each of 10 participants after they smoked a cannabis cigarette. The stabilities of Δ(9)-tetrahydrocannabinol (THC), 11-hydroxy-THC (11-OH-THC), 11-nor-9-carboxy-THC (THCCOOH), cannabidiol (CBD), cannabinol (CBN), THC-glucuronide, and THCCOOH-glucuronide were determined after 1 week at room temperature; 1, 2, 4, 12, and 26 (±2) weeks at 4 °C; and 1, 2, 4, 12, 26 (±2), and 52 (±4) weeks at -20 °C. Stability was assessed by Friedman test.
Results: Numbers of THC-glucuronide and CBD-positive blood samples were insufficient to assess stability. In blood, 11-OH-THC and CBN were stable for 1 week at room temperature, whereas THC and THCCOOH-glucuronide decreased and THCCOOH increased. In blood, THC, THCCOOH-glucuronide, THCCOOH, 11-OH-THC, and CBN were stable for 12, 4, 4, 12, and 26 weeks, respectively, at 4 °C and 12, 12, 26, 26, and 52 weeks at -20 °C. In plasma, THC-glucuronide, THC, CBN, and CBD were stable for 1 week at room temperature, whereas THCCOOH-glucuronide and 11-OH-THC decreased and THCCOOH increased. In plasma, THC-glucuronide, THC, THCCOOH-glucuronide, THCCOOH, 11-OH-THC, CBN, and CBD were stable for 26, 26, 2, 2, 26, 12, and 26 weeks, respectively, at 4 °C and 52, 52, 26, 26, 52, 52, and 52 weeks, respectively, at -20 °C.
Conclusions: Blood and plasma samples should be stored at -20 °C for no more than 3 and 6 months, respectively, to assure accurate cannabinoid quantitative results.