Law enforcement officers in Iowa and across the United States may ask you to submit to a breath test if you are pulled over on suspicion of drinking and driving. Officers use these roadside devices to determine whether you are driving with a blood alcohol content level that is at or above the legal limit of 0.08. 

Breath test devices determine BAC levels by measuring the amount of ethanol alcohol in an exhaled breath sample. Yet, studies show the results from these devices are not always accurate and could be unreliable. A breath test reading error may lead to wrongful DUI charges. 

Breath tests vs. blood tests 

After breath test devices measure the ethanol alcohol in the breath sample, it converts that number to a BAC level. Blood tests, on the other hand, obtain BAC levels by measuring the blood directly. Yet, the BAC levels obtained from blood tests can have a wide variance when compared to breath test readings. 

According to the State University of New York at Potsdam, breath test readings and blood test results may vary by more than 15%. That means one in four people who take a breath test will have results that are higher than their actual BAC level. 

Factors that influence results  

One reason for this variance is attributed to the fact that breath test devices often pick up other methyl groups that may be found in other substances. There are several factors that influence breath test results, including the following: 

  • Cigarette smoke and pollution 
  • Fumes from cleaners and gasoline 
  • Food, drink, vomit and blood left in the mouth  
  • Electrical interference from officer radios’ or cell phones 

In some cases, people who had not consumed any alcohol had a BAC level of .05 after eating certain breads. One participant was asked to apply contact cement to plywood and then paint a wall for an hour. The participant was asked to take a breath test 20 minutes afterward, and had a BAC level of 0.12. 

It is critical that officers know how to use breath test devices properly and calibrate them consistently in order to maximize the accuracy of results.