Are chemical breath test results usually accurate?

Police officers who believe that a driver is under the influence of alcohol at the wheel can collect several types of evidence. Often, officers follow motorists in traffic to record dashboard camera footage of their questionable driving skills.

Police officers also typically ask questions about prior behavior, including drinking habits, during a traffic stop. The answers to those questions can strengthen their suspicions of alcohol impairment. During a traffic stop, a police officer may ask a motorist to exit their vehicle to perform field sobriety tests.

If a driver fails field sobriety tests, then the police officer may have grounds to arrest the driver. Once they can arrest the driver, they then also have the authority to request a chemical test. Roadside breath tests are often a key component of the state’s case against an allegedly drunk motorist. Yet, breath tests are less accurate than the average person might realize.

False positives are a common issue

While chemical evidence is compelling, it is not without limitations. Chemical breath tests work by analyzing a sample of exhaled air. The test device looks for specific types of compounds, including alcohol.

However, other chemicals, such as acetone, can produce a false positive on a breath test. A person experiencing ketoacidosis due to a specialized diet or unmanaged diabetes could fail a breath test despite being sober. The use of breath sprays containing alcohol or even an asthma inhaler could undermine breath test accuracy.

Calibration issues with breath tests or mistakes while administering the test can also undermine the accuracy of test results. False positives and elevated test results are common enough that some courts in the United States no longer accept drunk driving cases where the only evidence the prosecution has is a failed chemical test. Drivers confused by the fact that they failed a breath test may have more options for fighting pending drunk driving charges than they initially realize.

It is possible to fight drunk driving charges if motorists have a credible explanation for why they failed breath tests during a traffic stop or after a crash. Reviewing a related situation with a defense attorney could help people identify explanations for a failed test other than alcohol intoxication. Those hoping to exonerate themselves may require support as they review the state’s charges and their personal circumstances, and that’s okay.