How Urine Drug Testing For THC Works

How Urine Drug Testing For THC Works

Your quick guide to understanding urine drug testing for cannabis use.

Urine Drug Testing for Cannabis Use

Let’s start with an infographic to give a quick overview:

Infographic-urine-drug-testing-marijuana

Specimen Validity Testing

After collection of the urine sample, the first thing a lab will do is check whether it is a valid urine specimen. They want to make sure you didn’t substitute the urine for something else or add anything to it. They may check the following:

  • Color and appearance: Urine should have normal color and not be cloudy.
  • Temperature: Urine should be within normal body temperature range.
  • Creatinine: This is a by-product of protein metabolism. Low levels of creatinine may indicate that specimen is not real urine or that it has been diluted.
  • Specific gravity: This tests the density of urine. Similar to creatinine, it ensures that specimen has not been overly diluted.
  • pH: Urine should be within normal pH range, as extremes of pH will interfere with the drug tests.
  • Adulterants: Adulterants are any substance added to the urine to cause a false negative on the drug test. Many oxidizing agents (e.g. bleach) will do this. Common adulterants are now tested for by many labs, although what specifically they test for may vary.

Types of Tests for Cannabis Use

Urine drug tests for cannabis use do not test for THC itself since little THC is actually excreted into the urine. Rather, they test for metabolites of THC, which stay at detectable levels for much longer (It may help to be familiar with the basics of THC metabolism and elimination).

There are two types of tests that are used to assess cannabis use:

  • Immunoassay test
  • GC-MS test

The immunoassay test is used as a rapid and cheap screening test. This is the same type of test that is used in home drug testing kits.

So why don’t drug testing companies just use the immunoassay test by itself? The problem is that it produces a high rate of false positives  – it gives a positive result for cannabis use even when you have not ingested any cannabis.

The drug testing companies are obligated to use GC-MS as a confirmatory test to ensure you have actually used cannabis. The confirmatory GC-MS test is extremely specific – it produces almost no false positives.

So why don’t drug testing companies just use the GC-MS test? It uses expensive equipment and is much more time consuming. Companies would either need to charge more for drug testing or accept a much lower profit margin.

[Now that you know the basics of how the tests work, you can read the THC Detox Protocols to understand your detox options.]

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