How Do Drug Tests Work?

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Some companies and organizations may opt to test a person's urine, blood or saliva for evidence of recent alcohol or drug use, both illegal and prescription. There are several instances in which drug testing can take place. An organization may offer assistance in support of treatment if a drug test is positive, but evidence of drug or alcohol abuse may also result in termination or arrest.

How Do Urine Drug Tests Work?

Urinalysis is the most popular form of drug testing. A urine test shows metabolites, or markers, that are produced as the body processes the drug. These compounds can remain in the system days or weeks after the effects of the drug have worn off. A positive test result is evidence of drug use, even if the person tested hasn't used that day. Urine tests work better with drugs than with alcohol, which passes through the body too quickly to gauge an accurate reading.

There are two types of urine tests. An immunoassay test is cheap and gives quick results. However, it doesn't pick up on all drugs and sometimes yields a false positive conclusion. A chromatography/mass spectrometry (GC/MS) test is administered to confirm the results of a positive immunoassay test. While more costly with a longer wait time, the GC/MS is more accurate.

To take the test, the subject produces a urine sample in a cup and must provide at least 45 milliliters of fluid to detect metabolites in the system.

How Do Blood Drug Tests Work?

A blood test is a more accurate indicator of recent drug and alcohol use than urine, as it measures the amount of alcohol or drugs in the blood at the time of testing, rather than inactive metabolites created by the body's processing of a substance as urine does. Blood samples are taken from a vein on the inside of an arm, the back of the hand or from the finger using a fingerstick.

Despite its accuracy, blood testing is used less than urinalysis as it has a shorter window of detection. Most drugs and alcohol pass out of the blood in about six hours. Blood tests are also more expensive, and there is a longer waiting time for results.

A blood test is also used in cases of severe injury or death to determine the level of intoxication at the time of the incident.

Read More: What Is a Non DOT Drug Test?

How Do Saliva Drug Tests Work?

Saliva tests are inexpensive and yield on-the-spot results. Saliva is taken from the mouth via a swab or stick and placed on a test strip, which changes color or shows lines if drugs or alcohol are present in the system. A saliva test does not need to be sent to a lab for completion, making it the perfect option for law enforcement officers who need results quickly, as in cases of impaired driving or machine operation. As with blood, the presence of drugs in saliva is shorter than it is in urine and the test is more accurate in determining current use.


  • A company can test for substance abuse before hiring an employee or as a random event once the person is on the job. Sports organizations often test athletes for banned or illegal substances, and law enforcement agencies may test for proof of impairment while driving or after an accident.