If you are suspected to be under the influence of marijuana, how can authorities test for it? What tests are done and what do those tests show?
Presumptive Testing
The most common way to test people for pot use is enzyme immunoassay (EIA). The test identifies the presence of THCCOOH, which is a marijuana metabolite, not even THC itself. The test determines that you had THC in your system but doesn’t test for active impairment. It isn’t concerned with the concentrations present.
The test will also pick up other cannabinoids because of cross-reactivity. Test results are given in terms of total cannabinoids in the person’s system. This means that you may fail a drug test even if taking CBD extract that is 100% THC free. Any result of more than 50 ng/mL results in a failed test.
Definitive Drug Testing
There are times when a more accurate result is required. Gas chromatography-mass spectrometry (GC-MS) or Liquid Chromatography with tandem mass spectrometry (LC-MS-MS) are both used. These tests give identification confirmation. What these tests find are dependent on the limits of the sample that is used.
What do they test?
What you are testing tells you different things. The samples urine tests are enough to tell if the test subject has taken THC recently. Urine tests will only test for THCCOOH. Urine tests are preferred because they are cheap, reliable enough for most uses, and obtaining the sample is simple and non-invasive.
Blood tests will test for THC as well as THCCOOH and 11-OH-THC. Testing blood is better when screening for active cannabis use because active THC can be directly detected. These tests aren’t as common because they are invasive and required a more skilled technician. The difficulty in administering the test is the largest barrier.
Testing hair will detect the presence of all three chemicals as well. Since it takes time for the THC to make its way into the hair follicles, testing hair isn’t to measure if someone is currently using the drug. Hair is a better long term test because the hair will keep a record as long as it is growing.
Saliva can be tested directly for THC. The test is only for current use. THC will only show up for several hours to a day at the most.
