Alcohol Testing Procedures

Alcohol testing is performed on people for different reasons and in different ways. Suspected drunk drivers or high school students may be required to take a breath-analysis test, and people on probation sometimes have blood drawn to check if they've been drinking against the terms of their release.

Breath Test

• Breath tests use one of three technologies to measure the alcohol content of a person's breath.

  Spectrophotometers most often are found in desk-mounted breath testers, such as the ones used in police stations. They shine infrared light on the breath molecules, which helps calculate the level of ethanol. This helps determine a person's alcohol level.

  Fuel-cell testers are more portable. They oxidize the alcohol in the breath sample and produce an electrical current. The greater the current, the higher the person's blood-alcohol content.

  Semiconductor oxide testers use an ethanol sensor to measure the BAC. They are small but require more calibration than fuel cell testers.

Urine Testing

• Urine testing is a common method to screen for illegal drugs. While a positive result does show that alcohol has been in the person's system recently, it does nothing to reflect that person's current state. For this reason, urine testing often is used for situations where a person is not allowed to drink at all (such as probation).

  Urine testing requires the subject to urinate into a cup. It often is done in private, though in a legal context such as probation, an officer might be present to ensure that the subject is not cheating.

Blood Testing

• Once blood is drawn, it is sent to a laboratory for testing. The laboratory mixes the sample with propanol or butanol, then heats it to produce a vapor. The vapor is passed through a glass column and measured as it passes through the other end. A machine called a chromatograph measures blood alcohol and produces the results on a chromatogram, which resembles an EKG reading. Chromatographs must be calibrated regularly, and the glass columns must be replaced to produce accurate results.

Hair Testing

• Hair testing is a relatively new method of alcohol screening. Using a hair sample, the test can trace a person's alcohol-use history by detecting derivatives of fatty acids that the hair produces after alcohol use. Hair-test developers say the screening method is useful for determining long-term patterns of drinking.

Saliva Testing

• Saliva tests report recent alcohol use, and are common in workplaces and rehabilitation centers. These are sold in kits. The subject takes a saliva sample with a swab, which is then inserted into a testing device that produces a readout of the person's alcohol level.