How Does a Swab Drug Test Work?

Oral fluid drug tests are a popular choice with employers and with parents who want to test their teens for drugs. Among oral fluid drug tests, the swab type is the most common. The highly absorbent mucous membranes of the mouth and the nature of the glands that produce oral fluids allow swab drug tests to be surprisingly accurate.

Sample Types

The term “oral fluids” refers to more than merely saliva, but saliva is the most abundant of the oral fluids. For this reason, oral fluid drug tests are often called “saliva tests” or “spit tests.” Oral fluid samples may be retrieved in two general ways: spitting and swabbing. While swab tests do not allow multiple tests to be performed on the same sample, they make it easy to collect samples without contamination and provide easy, fast, accurate results.

Clinical Setting

When a swab drug test is used in a clinical setting, a multi-purpose medical swab may be used to collect the sample. A medical professional places the swab between the subject's cheek and lower gum or under his tongue and holds it there for several minutes. The clinic then sends the swab to a lab, where it is tested for the presence of target drugs.

Swab Drug Kits

When a swab drug test is performed by an employer or parent, they generally use a commercially-available drug testing kit. The collection device, which is similar to a pregnancy test, contains an absorbent strip housed by a thin, plastic casing. The swab device is placed in the same manner as a clinical swab in order to collect the sample. The “lab” is built into the device. As the sample is absorbed, a colored control line “floats” higher or gradually appears in the device window.

Reading Test Results

With a testing kit, one or more lines indicates whether a certain type of drug is present. In the case of a multiple-drug array, each drug is represented by a different color. If the line appears, the drug is not detected. If a line is missing from the array, it is considered a positive result for the presence of that drug. Electronic versions don't require the reading of lines. Instead, the presence or absence of the target drugs is indicated on a clear, electronic readout.

Drug Detection

Most swab drug test kits test for a standard array of drugs, which may include the following “parent drugs”: amphetamines, methamphetamines, cocaine, opiates, THC (marijuana-type drugs), phencyclidine, benzodiazepines and methadone. The test does not indicate the presence or absence of a specific drug in the system (e.g., heroin); it only indicates the parent drug (in this case, opium).

Advantages

Swab drug tests are inexpensive and provide quick results on a wide range of drugs. They are easy to use and generally easy to read. Moreover, they sidestep some of the common problems involved with other methods. Samples can be collected “on the spot,” without the modesty issues inherent in urine sample collection. This allows observation throughout the testing procedure and virtually eliminates switching, diluting or tampering with the sample.

Disadvantages

While other samples provide a longer history of drug use prior to test administration, oral fluid tests will only indicate drug use in terms of very recent use (typically 24 to 48 hours). Also, while swab tests check for a wide range of drug types, they do not test for some of the most commonly abused drugs, such as alcohol or inhalants.