How Does a Drug Test Work?

How Does a Drug Test Work?
How Does a Drug Test Work? (Image: Drug Test Systems)

What a Drug Test Does

Drug testing is done to determine if there has been recent usage of the following five drug groups: cocaine, amphetamines, opiates, phencyclidine, and cannabinoids (which includes marijuana and hash). There are some drugs that are excluded, including but not limited to semi-opiates such as oxycodone, oxymorphone, hydrocodone and hydromorphone. There are several ways to conduct drug tests, including oral/saliva, hair, sweat and urine.

Oral/Saliva Testing

Oral or saliva drug testing has become increasingly popular because it is a non-invasive way to collect a sample and test for drug use. A swab in the shape of a toothbrush but with a pad instead of bristles is used to collect the saliva. The swab is placed between the lower cheek and gum for about 2 minutes and then placed into a vial once saturated. It is then tested using a drug testing kit and results are given within minutes.

Because they are easy to administer, oral testing is done frequently in the workplace. The limitations in this exam include only being able to test for very recent drug use, as in the last 3 to 4 days. This form of exam can test up to 8 different kinds of drugs, though testing is done for about 5 to 6 different drugs at one time. It is best used for drug use in the last month or so. Further, this examination gives a false positive for specific kinds of drugs and many of today's designer drugs are not accounted in this exam.

Urine Testing

Urine testing is another popular form of drug testing. It requires either a urine sample or the use of a test kit or a laboratory exam. After collection, the urine sample is placed on a test card and the test card is then tested for drugs on site with immediate results. A laboratory exam consists of using the gas chromatography and mass spectrometry analysis (called GCMS test).

Test results vary based on the body, age and size of the person. Cheating of this test is often done, reducing its accuracy. Cheating can occur with detox and other products that flush out the drugs.

Spray/Sweat Testing

Spray or sweat testing is done by applying a patch to the skin for 10 to 14 days in a manner similar to using a bandaid. The patch is sent to a lab at the end of the designated time period and tested there. The lab tests the sample using the GCSM test just as the urine drug test. This test only detects drug usage during the time the patch was worn.

It is usually done in the case of child protective agencies or parole departments and government agencies. The sweat/spray test is the least favorable of all of the exams and has been considered the least stable of all drug exams. Peer review and legal reviews have questioned its validity and appropriateness and suggest that this exam has a higher risk of false positives. Fortunately, confirmation tests are also done in the event of a positive test result.

Hair Testing

Hair testing is considered the most accurate because it can test drug usage for up to 90 days. A sample of the hair is collected from the scalp and sent to the lab for a GCMS test similar to the urine and sweat drug tests. The sample of hair required is about 1 1/2 inches in length. Only the most recent 1 1/2 inches are tested and so the hair must be cut as close as possible to the scalp. Each 1/2 inch covers about 30 days, as normally our hair grows at a rate of 1/2 inch per month. Accommodations can be made for people with short hair and body hair can be used in place of the hair on the scalp. Hair cannot be taken from a hairbrush.

Hair testing is considered the most accurate because it covers the longest length of time. It is not affected by chemical hair treatments such as coloring. Further, shaving the head does not confound the test, however, washing the hair with lemon juice does. Hair testing is also used to test for alcohol in addition to drug testing.

Limitations In Drug Testing

Specific drugs vary in their detection periods. Most common drugs can take anywhere from 2 to 4 days before detection. Still, there are exceptions and these can take up to 14 days.

To discourage tampering and/or to reduce miscalculations, tamper evident kits are made. Further, labs usually do two tests of the sample, a screening test and a confirmation test.

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