Flawed Science: measuring my breath reveals what’s in my blood?

No, it doesn’t.

It’s reasonable to assume that if the government gives you a test to determine if you’ve broken the law, the test will be reliable and accurate. Unfortunately, this assumption is incorrect. The OWI breath test, routinely administered in traffic stops around Louisiana, is unreliable, according to research published in the Journal for Forensic Sciences. It’s not just the breath tests in Louisiana that are flawed; breath test technology simply isn’t advanced enough to give reliably accurate results, writes Dr. Michael P. Hlastala.

Testing blood alcohol concentration (BAC) based on breath samples has been around since the late 1930s, when Prof. Rolla H. Harger of Indiana University developed a device called the “drunkometer.” Drivers whose breath registers above a certain BAC face prosecution, and certain “presumptions” of intoxication attach to the result. These laws, referred to as per se statutes, do not require proof that a driver’s ability to drive was affected by alcohol; simply that at the time he/she operated a motor vehicle he/she had a BAC above a set limit.

Hlastala says “the breath test is fairer for some subjects than others.” It might not be fair for you, but the same test might be fair for someone who is heavier, or has greater lung capacity, or who takes in more air when they inhale, or has some other physical trait more compatible with the test that measures alcohol content in exhaled breath. In fact, writes the doctor, the alcohol contained in exhaled air is more an indication of a person’s breathing patterns than it is the alcohol level in their system. That’s why there is such “a large variation” in test results: the test is dependent on how you breathe, not on how much alcohol you’ve consumed or how impaired you might be.

Adding insult to injury is that Louisiana is one of the few states in this country that use only a single test result to prosecute its citizens. In October 1986, over 30 years ago, the National Safety Council comprised of the most respected scientists in our country recommended that at least two breath samples be collected (between 2 and 10 minutes apart after an initial 15 minute observation period). This recommendation has remained unchanged and was reurged in February 2015. The scientific community remains in agreement that breath testing for alcohol using a single test method should NOT be used for scientific, medical or legal purposes where accuracy is important.

Hlastala suggests that lawmakers reevaluate the legal significance the test holds in court: “Given the variation in the breath alcohol test, it might be appropriate to consider decreasing the importance of threshold levels for penalties.” In other words, reduce the penalties given to people who “fail” the flawed breath test to determine blood alcohol content (BAC); and, in Louisiana, force law enforcement officer to administer two tests. Better yet, it might be time to shelve the defective test and develop new, reliable technology.

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