The Johnson Law Firm, LLC

Are breath tests accurate in determining BAC?

When a Missouri police officer pulls you over on suspicion of driving while intoxicated, you likely will have to take a breath test. You may fear that complying will incriminate yourself and therefore decide not to take the test. Your refusal will cause you to automatically lose your license for a year.

Although you can appeal this penalty, it can be easier for your criminal defense attorney to fight the results of the breath test instead. Many factors contribute to the inaccuracy of breathalyzers, making them not as solid evidence as police think they are.

How breath tests work

An officer will ask you to blow into a device to estimate your blood alcohol content. The key word here is estimate. Unlike blood tests, breath tests do not measure the exact percentage of alcohol in your bloodstream but rather base it on the partition ratio of the alcohol vapor you exhale. The reading therefore comes with a margin of error, the amount which depends on the quality and administration of the device.

Factors that lead to inaccurate results

The roadside breathalyzers law enforcement uses are high quality, but they are still susceptible to internal and external error. Some of the things that make BAC appear higher than it really is include:

  • Infrequent or incorrect calibration: Not calibrating the instrument regularly or properly leads to inaccuracy and inconsistency.
  • Insufficient training: Police must undergo thorough training on how to care for and use breathalyzers.
  • Presence of foreign substances: Things such as mouthwash and medicine can lead to false positives. Even fumes in the air and radio interference can cause inaccurate results.
  • Physiological traits: Your gender, weight and even body temperature all can affect the reading.

These all reveal how a breath test may not show how intoxicated you really are, and when it comes to DWI, one-hundredth of a percentage can make all the difference in your case.

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The Johnson Law Firm, LLC

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Saint Peters, MO 63376

Toll Free: 877-244-1187
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