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How accurate are DUI breath tests? Not very

DUI breath testing is prone to a wide variety of errors.  Just because your DUI breath test said your BAC was above California's .08% legal limit, that doesn't mean it was right.

DUI blood tests are generally considered more reliable than DUI breath tests.  Nevertheless, most people arrested for DUI in California opt for the convenience of a breath test.

Breath tests, however, are prone to numerous errors that can result in falsely high blood alcohol content (BAC) readings. And unlike blood samples, breath samples cannot be preserved for retesting later on.

An experienced DUI defense lawyer, however, has other ways to challenge the results.

1.   Operator Error

Often a DUI breath test will show a BAC over the California legal limit due to the simple failure of the operator of the testing device to conduct the test properly.  Errors operators often make include:

  • not checking your mouth to ensure it is empty before administering the test,
  • failing to observe you continuously for a full 15-minutes before beginning the test,
  • not recording the time at which the 15 minute period started,
  • failing to get at least two "blows" with consistent BAC readings,
  • not recording the time at which each “blow” was made, or
  • improperly attaching the mouthpiece to the machine.

2.   Laboratory Errors

California law also regulates who can give you a DUI breath test and how testing devices must be maintained. In addition to operator error, sources of falsely high BAC readings can include:

  • improperly trained breath testing device operator,
  • testing device not properly or regularly calibrated, or
  • poor record-keeping by the lab.

3.     Medical Conditions

Not all falsely elevated BAC readings result from operator or procedural error. Certain medical conditions or diets can “trick” breath testing devices into false positives. These conditions include:

4.     Residual Mouth Alcohol

Breath testing devices work by measuring the concentration of alcohol in the deep lung region called the "alveoli." The concentration of alcohol in this “deep lung air” corresponds roughly to the amount of alcohol in your blood.

When you consume anything containing alcohol, however, some of the alcohol remains in the mucosal linings of the mouth. This is known as “residual mouth alcohol.”

Residual mouth alcohol can produce falsely high BAC readings.  Even if you are not yet drunk because your system has not yet fully absorbed the alcohol (“rising blood alcohol”), you might test over the legal limit. Sources of residual mouth alcohol include:

  • a recently consumed alcoholic drink (“one for the road”) – even if you aren't legally drunk,
  • cough syrup, or
  • mouthwashes or breath sprays containing alcohol.

5. Miscellaneous Factors

Breath testing equipment has become more sophisticated in recent years. But certain extraneous factors can still affect DUI breath test machines, including:

6. Common California DUI Breath Testing Equipment

Our Los Angeles DUI lawyers understand the science behind DUI breath tests. We have successfully challenged DUI breath test results for clients throughout Los Angeles, Riverside, San Bernardino, Ventura and Orange Counties.

Don't let a falsely high DUI breath test stand between you and your good reputation.  Contact us for a free consultation today.

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DUI cases are rarely hopeless. DUI convictions are almost never inevitable. Clients retain our California DUI defense attorneys for one reason: they want to fight the case. And win.

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The police arrested you for DUI. You gave a blood or a breath sample. The DUI officer confiscated you drivers license. The police released you with a notice to appear in court in a few weeks. Where do you go from here? Our lawyers are here to guide you step by step.