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Home Blog Can I Really Challenge a Breath Alcohol Test?

Popular opinion often sways us more than we realize.  For example, many people believe that if a police officer gives you a breath or blood test to determine your intoxication level and the results come back as .08 percent blood alcohol content or higher, your DUI case is “open and shut.” These people are often surprised to learn that blood and breath alcohol testing is successfully challenged every day in courtrooms across the country, and that people who were told they were legally drunk have been able to argue flaws in the tests that resulted in dismissal of the charges.

How Do BAC Tests Work?

In order to understand how a blood or breath alcohol test could be wrong, you must first understand how the tests work.  The tests for blood and breath alcohol level operate on different principles, so it is important to know which you were given and how the results are tabulated.

Breath tests work on a density principle.  When blood flows through the lungs, any alcohol in the blood will be dispersed into the lung’s alveolar air and exhaled.   While the density of alcohol in the breath is not the same as that in the blood, an accepted ratio is 2,100 mL to one.  This means that 2,100 mL of alveolar air has about the same alcohol concentration as one mL of blood.  This ratio makes it easy to calculate a blood alcohol density level from expelled air.

The breath test machine checks for exhaled alcohol.  Alcohol that is contained in the breath is analyzed through a chemical reaction, infrared spectroscopy or a fuel cell.  No matter which method is used, the machine gives a reading that indicates the final blood alcohol content analysis.

Are Breath Tests Always Right?

As with any test, there is the possibility of error.  If an officer gives the test incorrectly, the conclusions may be wrong.  Breath tests can also be affected by alcohol still in the mouth, by certain medications and other factors.

Alex Lane has more than 13 years of experience as a criminal and DUI defense attorney.  When someone comes in with a DUI charge based on a breath test, Mr. Lane will work hard to ensure that the test results are held up to the highest possible scrutiny and that the accused person is given a fair opportunity to challenge the test.


If you have been charged with a DUI, drug charge, sex crime or any serious criminal offense, let an experienced defense team fight for you. Schedule a consultation with one of our partners today. Call (480) 562-3482 or send an email.