Are positive breath tests accurate indicators of intoxication?

Law officers use breath tests to find drivers’ blood alcohol levels. Yet, studies show the results to be unreliable.

Law enforcement officers in North Carolina and across the nation use roadside breath test machines to help them determine if a driver is operating a vehicle while intoxicated. Drivers who do not cooperate with officers who wish to administer a breath test may face certain penalties. However, evidence gathered by researchers indicates that the results from breath test machines are not always reliable. In some cases, inaccurate readings from these devices may cause an officer to arrest and charge an innocent person with drinking and driving.

Breath test devices: How they work

Breath test devices use the driver's exhaled breath sample to calculate how much alcohol is in his or her system. The machine then takes the breath alcohol content and converts it into a blood alcohol content level. When researchers compared the blood alcohol content level obtained from a breath test device to the BAC level measured directly from a blood test, they found a 15 percent variance, according to the State University of New York at Potsdam. This means that even a person who has an actual BAC level that is below the legal limit of 0.08 percent may have a breath test reading that measures over the legal limit.

What factors can affect breath test readings?

Breath test devices identify more than just the amount of alcohol in a person's system. Breath test analyzers can pick up multiple compounds, such as food particles, blood, vomit and other residual chemicals in the subject's mouth.

Other environmental factors can also affect the accuracy of a breath test reading. These include but are not limited to the following:

  • Relative moisture in the air
  • Ambient temperature
  • Fumes from gasoline, cleaners and/or paint
  • Interference from officers' hand-held radios and cellphones

A number of officers may hold the breath test device wrong or fail to calibrate it regularly, thereby affecting the accuracy of the results it provides.

Case in point

One study measured a participant's blood alcohol level using both a blood test and a breath test after he was exposed to spray paint fumes for approximately 20 minutes. Although the man was wearing a mask during the exposure, the breath analyzer results showed his BAC level to be .075 percent. The blood test, on the other hand, reported no alcohol in the subject's system.

Facing DUI charges

Having a DUI on your record can affect your life in many ways. You may have difficulties finding a job in certain industries, applying for a loan or getting a driver's license. If you have been charged with a DUI, you may want to seek assistance from a criminal defense attorney in North Carolina.