Cannabis-Related Disorders Workup

Updated: Mar 23, 2017
  • Author: Lawrence Genen, MD, MBA; Chief Editor: David Bienenfeld, MD  more...
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Workup

Laboratory Studies

Urine testing

Cannabinoids can be detected in the urine for as many as 21 days after use in persons chronically using marijuana, because these lipid-soluble metabolites are slowly released from fat cells into the blood; however, 1-5 days is the normal urine-positive period.

The primary method for urinalysis detection is enzyme immunoassay or radioimmunoassay. This method is inexpensive, quick, and accurate. This is also useful for confirmation of abstinence.

Urine samples are difficult to obtain from people who are addicted, and providing a urine sample is easily evaded. Urine toxicology testing should be performed under supervised conditions to ensure reliability of results.

Gas chromatography in combination with mass spectrometry and/or thin-layer chromatography is used to confirm positive results, especially in legal proceedings.

With all types of tests mentioned, including thin-layer chromatography, false-negative results tend to be more common than false-positive results.

Blood testing

Blood samples may be used to measure quantitative levels of cannabinoids. [31] Serial monitoring of tetrahydrocannabinol (THC)–COOH to creatinine ratios can distinguish between recent use and residual excretion. To assess the extent of cannabis use, determination of free and bound THC-COOH can be useful.

Blood analysis is the preferred method of detection for interpretation of acute effects. The cannabis influence factor is a tool used to interpret concentrations of THC and its metabolites in forensic cases. Absolute driving inability has been proposed in the case of cannabis influence factor of 10 or higher. The higher the cannabis influence factor, the more recent the cannabis abuse.

Blood samples must be taken within a prescribed 8-day period, and THC-COOH concentration greater than 75 ng/mL is associated with regular consumption of cannabis. THC-COOH concentration less than 5 ng/mL is associated with occasional consumption.

Hair analysis

Hair analysis is not a sensitive enough tool to detect cannabinoids. [31] THC, and the main metabolite THC-COOH, do not incorporate to a great extent into hair. TCH-COOH is not highly bound to melanin. Hence, concentrations in hair are much lower when compared with other drugs of abuse. Because TCH is present in cannabis smoke, it can also be incorporated into hair simply by second-hand exposure.

Saliva testing

Saliva testing is a newer technology for detection. The presence of delta-9-THC in oral fluid is a better indication of recent use than the presence of 11-nor-delta-9-THC-9-COOH detected in urine. Therefore, the probability that a user is experiencing effects is higher. This may prove especially useful in the monitoring of driving while under the influence.

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Imaging Studies

Although no confirmatory imaging study exists for marijuana use, pilot investigations involving neuroimaging of marijuana smokers performing various mental tasks have revealed many differences in comparative levels of activity in many regions of the brain with respect to controls.

Functional MRI and diffusion tensor imaging techniques demonstrate significant differences in the magnitude and pattern of signal intensity change within the anterior cingulate and the dorsolateral prefrontal cortex while performing standardized tasks in chronic marijuana smokers compared with healthy controls.

Neuroimaging studies, such as CT scanning, MRI, and positron emission tomography scanning, are extensively used to study the neurobiological effects of cannabis abuse but are not clinically useful in the definitive determination of recent abuse.

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