Breath test device results: Are they truly accurate?

On Behalf of | Dec 17, 2020 | Dui / Dwi |

When law enforcement officers pull people over on suspicion of drinking and driving, they often use breath test devices to measure their blood alcohol content level. Along the roadside, it is impractical to get a blood sample in order to determine a BAC level. However, there are differences when comparing the results from a breath test to those of an actual blood test.

According to researchers at the State University of New York at Potsdam, at least one in every four people tested with a breath test machine will have inflated BAC levels when compared to a blood test. Breath test readings may vary by more than 15% from blood test results as well. This can lead to a wrongful DUI charge and possible conviction.

How do breath test machines work?

When you blow into a breath test device, the machine detects ethanol alcohol in the sample. It then converts this amount into a blood alcohol content reading. Blood tests, on the other hand, measure the amount of alcohol in the blood directly, with no conversion factors and additional room for error.

What factors can alter the results?

The device picks up more than simply ethyl groups from alcoholic beverages. It also measures substances with similar methyl structures, and these substances can be found in many items people eat, drink and breathe every day. Factors that alter BAC level results include the following:

  • Dirt and pollution from the air
  • Relative humidity of the air
  • Gasoline fumes, cleaners and cigarette smoke
  • Residual food, blood, vomit and drink in the mouth
  • Personal hematocrit levels in the blood
  • Electrical and static interference from police radios and cellphones

Breath test devices must be properly maintained and calibrated regularly to maximize the accuracy of results. Furthermore, the officer administering the test must do so properly or it could lead to erroneous results as well.


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