Blood Test Versus Breath Test

Driving Under the Influence (DUI) is a criminal offense with significant consequences if convicted. If a police officer suspects you of a DUI, they may ask you to take a blood test or a breath test (breathalyzer) to obtain evidence to support their suspicion. Additionally, police may ask you to perform a field sobriety test, although these tests are subjective, relying on the arresting officer's judgment, and do not carry the same evidentiary weight as a breath test or blood test.

When an individual consumes alcohol, the liquid travels through the esophagus on its way to the stomach and small intestine before entering the bloodstream and making its way through the rest of the body. Eventually, the alcohol in the bloodstream will travel to the lungs and be expelled from the body in very small amounts each time a person exhales.

The effects of alcohol in the bloodstream can vary from person to person, ranging from reduced mental sharpness to impaired physical coordination. If your behavior while driving after drinking alcohol catches the attention of law enforcement, they may ask you to undergo tests to determine if you exceeded the legal limit and are driving impaired. In Tennessee, the legal limit is 0.08% for blood alcohol concentration (BAC) for adult drivers aged 21 and older.

Field Sobriety Tests

A police officer may request that you perform a physical test to assess aspects such as coordination, balance, mental ability, or vision. These types of tests can often be challenged more easily by a defense attorney than a breath or blood tests. With these tests, passing or failing is subjective, as it relies on the officer's opinion. At the time the field sobriety tests are performed, the officer is determining whether you have been drinking and might be over the legal limit. In reality, you might simply be tired, scared, uncoordinated, or have a medical issue, which could affect your performance to the officer's satisfaction.

Breath Test

Breath tests utilize a breathalyzer device to assess the amount of alcohol in a person’s bloodstream. The process involves inserting the device into the suspect's mouth, having them exhale into a tube, and then the device produces readouts of the individual's blood alcohol level.

Generally speaking, law enforcement officials favor breath tests because the device itself is easy to use and highly portable. It can be administered directly at the traffic stop. Although trained, police officers do not need a license or registration with any agency to use the device, and the device functions effectively in any setting without the need for a specific environment.

However, breath tests are not as reliable as you might believe or as the prosecutor might suggest. Environmental factors, like weather conditions, can adversely impact breathalyzer results. Recent food consumption can also alter the results. Even a swish of alcohol-based mouthwash can affect results. A skilled defense attorney can show the issues with the test results, arguing that it can not be relied upon conclusively for a conviction.

Blood Test

Of the two sobriety tests, blood tests tend to produce more accurate results. However, even blood tests can be shown to be unreliable.

Instead of measuring alcohol vapors in a person’s lungs, a blood test provides a more direct method for determining an individual’s alcoholic toxicity level. However, the equipment necessary to safely collect a blood sample and provide accurate result requires a controlled environment, making field administration improbable. Blood test can be conducted at the jail or possibly at a nearby hospital.

Blood test results may be challenged for things like method of extraction, blood sample storage, or blood sample analysis.

Contact Murfreesboro DUI Defense Lawyer

David Clarke is an experienced criminal defense attorney and is familiar with defending clients against DUI charges. To find out more about how our office can help in your DUI defense, contact us today at (615) 796-6299.