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Blood alcohol concentration (BAC) tests measure the amount of alcohol in your blood. They're usually used to determine whether you're driving under the influence (DUI). Field sobriety tests can give law enforcement officers conducting a traffic stop some indication as to whether you're impaired. However, they don't indicate what your BAC levels are. That's where BAC tests come in handy.

This article answers frequently asked questions (FAQ) regarding BAC tests. The article addresses the methods used to measure BAC and how Breathalyzer tests work. The article then covers the accuracy of BAC tests and whether it's possible to challenge Breathalyzer results in court.

What methods are used to measure blood alcohol concentration (BAC)?

Your blood alcohol content can be measured in multiple ways. To estimate your blood alcohol concentration, police can use samples of:

  • Urine
  • Saliva
  • Hair follicles
  • Blood
  • Breath

However, police officers typically only use breath analysis (i.e. Breathalyzer) and blood screenings for gathering evidence. Blood screening is considered more invasive and is used less often than breath analysis. Blood testing is mainly employed after a serious accident or when a suspect refuses a breath test.

How do Breathalyzer tests work?

Breathalyzers, or breath analysis machines, work by analyzing the alcohol content of exhaled vapor in your breath. Any alcohol from the vapors in your breath reacts with a chemical solution in the machine, creating a color change in the machine's reading. A computer translates the data into the BAC measurement used to determine the level of alcohol in your bloodstream (for example, 0.08 percent BAC).

How accurate are Breathalyzer tests?

While not as accurate as blood tests, most courts consider Breathalyzer tests acceptably accurate as tools for gathering evidence and determining impairment. However, some independent studies have determined that breath readings can vary by 15% from actual BAC levels as measured by a blood draw. Some courts have even thrown out Breathalyzer results, calling into question the reliability of the machines.

In 1988, a New Jersey court cited the following scientific evidence:

  • High readings for 14 percent of the population due to design flaws
  • Variance in results based on the temperature of the machine itself
  • Different results from the varying body temperatures of test subjects
  • Variances in the presence of hematocrit in the blood, affecting test results

Using an improperly calibrated machine can also hamper the accuracy of Breathalyzer test results.

Can you beat a Breathalyzer test if you're intoxicated?

No, you can't beat a Breathalyzer test if you're under the influence of alcohol. Some popular methods are commonly believed to help you fool a Breathalyzer test. These methods include:

  • Ingesting breath mints
  • Using mouthwash
  • Sucking on pennies

These methods, however, have been shown not to work. Mouthwash, which often contains alcohol, may actually raise your BAC.

Is it possible to successfully challenge Breathalyzer results in court?

Yes, it's possible to challenge Breathalyzer test results in court successfully. Breathalyzer machines must be tested routinely to make sure they're properly calibrated. A skilled DUI lawyer can look into the maintenance records of the device used to test you and otherwise determine the validity of the evidence.

How accurate are the small, inexpensive BAC-testing devices sold to consumers?

The accuracy of the small, inexpensive devices sold to consumers to test BAC levels depends on many factors. There is a wide range of products available. Some are more accurate than others. It's best to assume the readings on these devices are a little off and may not be used as a defense to DUI charges.

Saliva alcohol test strips are among the most accurate consumer BAC tests. This is because the amount of alcohol in your bloodstream closely corresponds to the alcohol concentration in your saliva.

Was Your BAC Test Accurate? A Defense Attorney Will Help Challenge the Evidence

Understanding the science behind a blood or breath sample result can be challenging. A drunk driving conviction can carry serious consequences, including jail time, the loss of driving privileges, and a driver's license suspension. Contact a DUI attorney in your area to learn more about DUI laws and your options following a DUI arrest. A defense lawyer can help you with your DUI defense, whether you're a first-time offender or you've had a previous DUI conviction.

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  • Complex DUI situations usually require a lawyer
  • DUI defense attorneys can challenge Breathalyzer/Intoxilyzer or blood test results
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