Marijuana is the common name given to plants in the Cannabis genus. Plants in this genus are well known for their psychoactive properties. Delta-9-tetrahydrocannabinol, more commonly referred to as THC, is the principal psychoactive component of the cannabis plant.
More than 55% of THC is excreted in the feces, mainly as the metabolite 11-hydroxy-tetrahydrocannabinol (THC-OH). Approximately 20% is excreted in urine as free 11-nor-9-carboxy-tetrahydrocannabinol (THC-COOH) and THC-COOH glucuronide. In addition to being the predominant metabolite in the urine, THC-COOH has a long half-life of several days and even weeks in heavy users. This makes it ideal for analysis by confirmatory testing in clinical laboratories.
THC and THC-COOH are highly lipid-soluble, so they tend to accumulate in tissues. The slow redistribution back into the bloodstream contributes to THC-COOH’s long half-life.
In confirmation testing, a sample preparation step called alkaline hydrolysis breaks the glucuronide bond to convert the conjugated metabolites back to free THC, free THC-COOH, and free THC-OH.
Because marijuana has been legalized in many states, confirmatory testing may not be needed in all cases. Labs should consider having two testing options: one in which positives are confirmed and another option in which a positive is not confirmed. In many instances, patients will admit to using THC. For such patients, an expensive confirmation test is hard to justify.
