Skip to Main Content

Are BAC Tests Unreliable to Determine DWI?

Posted by | June 12, 2015 | BAC Tests, DWI | No Comments
DWI breath test

The biggest piece of evidence in any case of driving while intoxicated (DWI) is the results of a blood alcohol concentration (BAC) test. These are chemical tests that determine a driver’s BAC through their breath, saliva, or blood. Under Texas law, it is illegal for a driver to have a BAC 0.08% or higher. However, BAC tests have come under recent scrutiny and may not be a reliable way to test for DWI.

Types of BAC Tests

In suspected DWI cases, Texas police use two types of BAC tests: a DWI breath test and a DWI blood test. In a DWI breath test, the authorities have a person breathe into a Breathalyzer machine that determines the BAC from the breath and saliva. Typically, an officer will ask a person to submit to a breath test before arrest, but this is voluntary and the driver can legally decline. However, after the arrest an officer can get a warrant that compels the driver to breathe into the machine. In a DWI blood test, the police take a sample of blood to determine a driver’s BAC. This test must be performed at the police station or the hospital and cannot be done on the road. However, an officer can compel a DWI blood test with a warrant.

Why Tests are Unreliable

Breath tests for DWI, performed on the road or in a police station, have been criticized for inaccuracies when determining BAC. False BAC readings from Breathalyzer machines can result from minor technological interference, such as a cell phone signal. In addition, breath tests have been known to misread BAC if there are other substances in the mouth, like blood or vomit, and irregular breathing has misrepresented BAC results, as well. DWI blood tests have also been scrutinized for their flaws in reading the BAC of a suspected drunk driver. People with diabetes or high blood ketones, or those taking cough medicine or herbal supplements have all reported erroneous BAC readings on a DWI blood test. If an alcohol swab is used prior to the blood draw, it can also misrepresent the results. Finally, some blood tests only check the blood serum and not the entire sample. Studies have shown that testing the serum alone can produce BAC results up to 25% higher than testing the whole sample. Beyond technicalities in the tests, there are other reasons why BAC tests are unreliable methods of testing for DWI. These tests do not take into account the alcohol tolerance, age, gender, metabolism, or weight of the individual. They also fail to consider whether the person’s BAC is rising or falling at the time of the test. High stress levels, a person’s emotional state, food, and carbonation can all also affect the results of a DWI test.

Our Firm Can Help

Call us now or contact our office today if you failed a DWI breath test in Austin or had a forced blood draw for DWI. Our experienced defense attorneys at The Law Office Of Robert L. Buford are here to help protect your rights against unreliable DWI tests. Our experience as Austin DWI Attorneys can help with your situation.