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Interpretive Handbook

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Test 505331:
Drug of Abuse, Tetrahydrocannabinol Screen with GC-MS Confirmation, Urine

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Marijuana is 1 of the most widely abused drugs in the United States. It is the term for describing a leafy preparation of the plant Cannabis sativa used to produce psychic effects. A common method for the consumption of marijuana is smoking.

 

The primary component of marijuana is delta-9-tetrahydrocannabinoid (THC). It is the concentration of THC that determines the potency of marijuana.

 

Following consumption of the drug, either by inhalation or ingestion, THC is rapidly metabolized by the liver through 11-hydroxy-delta-9-THC to a series of polar metabolites, with 11-nor-delta-9-THC-alpha-carboxylic acid (THC carboxylic acid, THC-COOH) being the primary metabolite.

 

Approximately 80% of a dose of THC is eliminated during the first 5 days, with >65% being excreted in feces and approximately 20% excreted in urine. Depending on assay sensitivity, cannabinoid metabolites may be detected in the urine up to 10 days in occasional smokers and 30 to 40 days in chronic smokers.

Useful For Suggests clinical disorders or settings where the test may be helpful

Detecting drug abuse involving delta-9-tetrahydrocannabinol (marijuana)

Interpretation Provides information to assist in interpretation of the test results

The metabolite of marijuana (THC-COOH) has a long half-life and can be detected in urine for more than 7 days after a single use.

 

The presence of THC-COOH in urine at concentrations >15 ng/mL is a strong indicator that the patient has used marijuana.

 

The presence of THC-COOH in urine at concentrations >100 ng/mL indicates relatively recent use, probably within the past 7 days.

 

Levels >500 ng/mL suggest chronic and recent use.

 

Chronic use causes accumulation of the THC and THC-COOH in adipose tissue such that it is excreted into the urine for as long as 30 to 60 days from the time chronic use is halted.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Negative

EMIT cutoff concentration: 50 ng/mL

Positives are reported with a quantitative GC/MS result.

Clinical References Provides recommendations for further in-depth reading of a clinical nature

1. Moyer TP, Palmen MA, Johnson P, et al: Marijuana testing-how good is it? Mayo Clin Proc 1987;62:413-417

2. Baselt RC, Cravey RH: Disposition of Toxic Drugs and Chemicals in Man. 3rd edition. Chicago, Year Book Medical Publishers, 1989