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Blood tests vs. breath tests: A look at results

On Behalf of | Oct 29, 2019 | Firm News

When law officers pull people over on suspicion of drunk driving, they may ask the driver to submit to a roadside breath test. Officers use devices as a way to determine the drivers’ blood alcohol content level, as doing so is easier than administering an actual blood test. 

If you have ever used a breath test device, then you already know firsthand the process of blowing into a tube and waiting for your blood alcohol content level to appear. While people rely on breath test devices to yield accurate and reliable results, this may not always be the case. Studies show that breath test readings are not always accurate and may lead to a wrongful DUI arrest. 

How do blood tests compare to breath tests? 

According to the State University of New York at Potsdam, breath test readings may differ by at least 15% from BAC results obtained from a blood test. Officers obtain BAC results from measuring the amount of ethanol alcohol contained in an exhaled breath sample. This number is then converted into a blood alcohol content level. Yet, the results differ significantly when comparing the BAC levels obtained from a breath test device to those of an actual blood test. 

What factors affect the results? 

Several factors affect the results of breath test devices. These include the following: 

  • Relative humidity of the air and temperature 
  • Breathing cigarette smoke, dirt and pollution 
  • Cleaner, paint thinner and gasoline fumes 
  • Residual vomit, food, blood and drink in the mouth 

It is important that the breath test device is properly calibrated to ensure reliable results. In addition, the officer using the device must know how to properly operate the machine. It is critical that officers take into account all factors when processing the BAC levels for drivers. 

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