Is the Breath Test Accurate? A Spokane DUI Lawyer’s Perspective

How accurate is the breath test instrument on DUI arrests? What if the result is .10 or .11? Does that mean you are automatically guilty? What is the margin of error?

The breath test you take on the side of the road is not admissible in court. The test that matters is the BAC at the police station.

There are many things that can effect the breath test accuracy.  Let’s take a look at them one by one.


There are certain contaminants that can effect the accuracy of the breath instrument.  Acetone is one of those contaminants.   Acetone can be present on a person’s breath if they are diabetic or if they are fasting.  Exposure to certain paint thinners and chemical can also effect the breath instrument.   There are studies that show false readings as high as .40 for contaminates. (The legal limit is .08.)  DUI lawyers often see this in cases where people work around chemicals.

Breathing Irregularities

There are also certain breathing irregularities that can throw off the breath test by as much as 16 percent.  Holding your breath prior to the breath test can increase the alcohol reading, while hyperventilating can decrease the alcohol reading.  The temperature of your breath can effect the reading too, and the warmer  the breath, the higher the alcohol reading.  A fever can cause an elevated breath test as well, as can asthma, emphysema, or other such lung diseases.

Mouth Alcohol

If a person has alcohol present in their mouth, this can throw off the breath test result dramatically.  Alcohol can be caught in chewing tobacco and even in dentures or other dental work.  Mouth alcohol can also be a result of vomiting or belching, or a breath spray or mouthwash.

Keep in mind we are discussing the BAC instrument that DUI suspects blow into at the jail or police station.  The little portable instrument you blew into on the side of the road is not admissible.

A lot of times people think that a breath test result over .08 means that their case is over.  In reality there is a lot that a DUI lawyer can do, particularly with the help of a expert witness.

For more information, visit our webpage.  Steve Graham does DUI case in Spokane and the surrounding counties of eastern Washington.


3 Responses to “Is the Breath Test Accurate? A Spokane DUI Lawyer’s Perspective”

  • Ameila:

    Having a good DUI Attorney who know the ins and outs of the law can be very helpful when a breath test is what the charge is based on. Making a mistake either way can be very expensive. Found a good attorney at // has been very helpful.

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  • very interesting post, a lot of great information. thank you for providing this.

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Steve Graham is a criminal defense lawyer, and he splits his time between Spokane and Seattle, Washington. Visit his website by clicking:
Law Office of Steve Graham
1312 North Monroe Street, #140
Spokane, WA 99201
(509) 252-9167
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