THC Drug Test
A marijuana drug test is the technical analysis of a biological specimen, such as urine, blood, hair, sweat or saliva, to determine the presence or absence of the active ingredients of marijuana (mainly THC) or its metabolites (breakdown products).
The chemical name for THC is delta-9-tetrahydrocannabinol, or simply tetrahydrocannabinol, and its metabolites can also be identified with a marijuana drug test. It is possible to get a false-positive result which means that the THC test reads positive or is inconclusive although marijuana was not used. With current laboratory techniques, the results are usually conclusive for the presence or absence of THC and its metabolites.
How Long Will THC Remain In The System?
The period of time during which THC is detectable in your system depends on multiple factors include the duration, frequency and quantity of marijuana used. Due to varying cultivation techniques, the quantity of the active ingredient in marijuana may vary and more potent marijuana samples may be detectable for longer periods after using it.
Usually THC metabolites can be detected between 10 to 14 days after using marijuana. There have been reports of THC metabolites being detectable between 30 to 90 days after marijuana use in regular users. It is important to note that urine tests are usually conducted to test for the presence of THC metabolites which indicates marijuana use. Blood tests are conducted when the amount of THC still present in the system has to be ascertained.
Reasons for THC Drug Test
There are a number of reasons why a THC drug test will be requested.
- Screening for marijuana and other drugs prior to employment.
- Testing for marijuana is of special importance in people in sensitive positions such as security and those in the army.
- As a safety precaution in people who operate heavy machinery or drive vehicles.
- Random drug testing in schools, companies and government departments – to act as a deterrent for drug use.
- Drug users on parole may be required to take routine drug tests to prove that they are no longer using these substances.
Types of Marijuana Drug Tests
The urine test is based on detection of 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid (9-carboxy-THC), a metabolite of delta-9-THC, which is the primary pharmacologically active component of marijuana. The breakdown products of THC (its metabolites) can be detected in the urine days or even weeks after stopping its use, depending upon whether a person is an occasional or a regular marijuana user.
Urine tests may not be an indicator of current marijuana use but more of past drug use. The metabolites of THC are stored in fatty tissues of various organs and are slowly excreted through the urine. This is the reason for their detection in the urine even weeks after the cessation of marijuana use.
Urine tests are fairly accurate if careful lab assessment is done and false positive results are extremely rare. Previously drugs like ibuprofen was known to affect the marijuana test results but this has been overcome. It is highly unlikely to get a false-positive result for marijuana with any other substance use or abuse.
This is a screening test where urine samples are initially screened for THC metabolites.
The sample is mixed with a solution which contains a specific antibody (tagged with a fluorescent dye or radioactive substance) for the THC metabolites. The amount of metabolites in the sample is measured by noting the fluorescent light or radioactivity emitted.
This test is unable to distinguish between smoked marijuana and the synthetic preparation dronabinol.
Gas Chromatography-Mass Spectrometry (GC-MS)
This is a confirmatory test conducted on samples which test positive under the immununoassay test. The urine samples are subjected to a gas chromatography-mass spectrometry (GC-MS) test. This ‘double testing’ excludes the chance of getting a false-positive result.
Urine Test Results for Marijuana
The accepted cut-off value for THC metabolites in the urine is 50ng/ml (nanograms/milliliter).
Passive smokers of marijuana may test positive but the level of metabolites is not likely to be as high as 50ng/ml. In occasional cases it may reach as high as 25ng/ml but the level detected in passive smokers is usually much less.
Blood tests to detect marijuana use are done in specific cases such as a road traffic accident, autopsy and to check for intoxication. Blood tests can help to determine if the person is presently on marijuana since THC itself can be detected in the blood as well as its metabolites.
A positive result can be obtained within a few hours after marijuana use. Regular users may test positive even after a day or two.
Saliva/Oral Fluid Tests
This is a less expensive and more convenient method of testing for marijuana. It gives quick and accurate results and can detect recent drug use.
Metabolites may be detected in the saliva for 12 to 24 hours to a maximum length of up to 3 days after marijuana use. Specimens are more difficult to adulterate since they are obtained under direct supervision. It may prompt other tests like a urine or blood test.
THC reaches the hair through the blood vessels in the scalp and gets deposited within the hair shafts. It is one of the most reliable methods of drug testing and can determine long term marijuana use, even months after the last use.
A small sample of hair, about 50 to 80 strands of a minimum of one inch in length cut close from the scalp, is necessary for testing. Samples may not necessarily be taken from the head. Hair from any part of the body, such as the chest, armpits, legs or face can be used.
Spray or Sweat Tests
Spray or sweat testing is done by applying a patch to the skin for 10 to 14 days, after which it is sent to the lab for testing. Sweat patch testing has certain drawbacks as the amount of perspiration may vary according to the environmental temperature and physical activity. In addition, it is difficult to monitor the subject for this period of time and the patch can be tampered with.
The belief that using marijuana just before the patch is removed will not yield a positive result is untrue. The patch can detect marijuana use just a few hours prior to its removal.
Related Questions and Answers
- Does Marijuana Affect Blood Test? Other Medical Tests
- Marijuana Chest Pain After Smoking
- Does Second Hand Marijuana Smoke Affect a Drug Test?
Article reviewed by Dr. Greg. Last updated on December 17, 2011