Breath test reliability and blood alcohol levels

Breath test reliability and blood alcohol levels

On Behalf of | Nov 14, 2019 | Firm News |

Law enforcement officers in Wyoming and across the country often ask motorists to submit to a roadside breath test when pulled over on suspicion of drinking and driving. The test allows officers to measure drivers’ blood alcohol content level without taking an actual blood test, which would be difficult on the side of the road. The problem lies in the fact that breath test devices do not always yield accurate and reliable results. 

According to research performed at the State University of New York at Potsdam, one in four drivers who have their blood alcohol content level measured using a breath test device has elevated readings when compared to the BAC level results obtained from a blood test. In fact, when comparing the results obtained from a breath test device to those measured from an actual blood test, researchers found a variance of up to 15%. This difference is enough to wrongfully arrest someone for a DUI, even when she or he may not be above the legal limit. 

How do breath test devices work? 

Rather than measure the amount of alcohol in the blood directly, breath test devices measure the amount of ethanol alcohol found in an exhaled breath sample. It then takes the amount measured and converts it to a blood alcohol content level. Yet there are methyl structures found in other substances that breath test devices may pick up as ethanol. This can alter the accuracy of breath test readings. 

What factors affect breath test readings? 

In addition to other substances that challenge the accuracy of breath test readings, a multitude of other factors can affect readings, as well: 

  • Gasoline fumes, cigarette smoke and fumes from cleaners and paint thinners 
  • Residual food, vomit, blood and drink in a person’s mouth 
  • Static electrical interference from cell phones and police radios 
  • The air’s relative temperature and humidity 
  • Proper machine calibration 

It is critical that the officer using the device knows how to handle it properly for it to give reliable results.