When a Tennessee resident is suspected of driving under the influence of alcohol, it is necessary to ascertain the level of alcohol the individual has in his or her system at the time. Anyone with a blood alcohol level of .08 percent or above is considered to be legally intoxicated. Three different blood alcohol tests can be used to determine whether an individual is drunk -- they are the breath test, blood test, and urine test.
Most police officers perform breath tests, since the units required are portable and provide instant results. The machines measure the amount of alcohol filtered through the alveoli air sacs, which are located in the lungs, which then exits the body through a person's breath. These tests might be sufficient to be used as evidence of intoxication in court, but they can also be inaccurate. Various substances, such as glue or paint thinner in the environment or a person's diet, can skew the test results. Furthermore, the machine does not differentiate between people, and inaccurate readings can occur due to the averaging of test results.
Blood tests are considered the most accurate of the three tests. However, mistakes by lab technicians, faulty testing equipment and other factors can render the test results inadmissible in court. Urine tests are not as accurate as the other two, and due to the time it takes alcohol to be present in the urine, results are not as reliable as those from breath tests or blood tests.
Even though the potential for flawed results is always a concern, refusing to submit to blood alcohol tests could have additional ramifications for Tennessee residents, such as the mandatory loss of driving privileges. An accused individual's criminal defense counsel will have the opportunity to scrutinize the methods used for testing, the equipment and people involved, and any other factors that could make the results suspect. Protecting an individual's rights is the first priority. Thereafter, all of the available options based on the strength of the evidence prosecutors intend to present to the court will be considered.
Source: bactrack.com, "Three Types of BAC Testing", Accessed on Oct. 16, 2016