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Are Breath Tests a Reliable Measure of DUI?

If you have been pulled over on suspicion of drunk driving in Tennessee, you may have been asked to submit to a roadside breath test. Law enforcement officers often use these machines to determine whether you are driving with a blood alcohol content level that is over the legal limit of 0.08 percent. The problem lies in the fact that portable breath test devices do not always yield accurate results. In some cases, the device readings may be altered by another substance or other factors that could inflate the BAC level given on the breath test. This could result in a wrongful DUI charge and possible conviction.

According to the State University of New York at Potsdam, the BAC level obtained from a breath test device can vary by up to 15 percent from the BAC level obtained from an actual blood test. This is due to the fact that other substances can affect the reading. These substances include the following:

  •          Residual food, vomit or blood in the mouth.
  •          Breathing paint, gas or cleaning fumes.
  •          Pollution in the environment.
  •          Temperature and relative humidity of the air.
  •          Interference from cellphones and police radios.

If the machine isn’t calibrated correctly or the law enforcement officer administering the test does so incorrectly, this could affect the readings as well. Physical activity may lower BAC level readings on breath test devices by 11 to 14 percent. Blood tests seem to be the only reliable measure of BAC levels, but cannot be given alongside the road. 

This information is intended to educate and should not be taken as legal advice.