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By Vince Imhoff, Esq. & Dan Rhoads

A group of judges in New Hampshire was served several alcoholic drinks as part of an experiment that was intended to demonstrate the effectiveness of the Breathalyzer. One judge was given so many drinks that he became visibly intoxicated. When the judge blew into the Breathalyzer, the machine registered a score of 0.0. After a few more tries, the Breathalyzer gave the same result. Following the demonstration, at least one police jurisdiction in the state ceased using the Breathalyzer in favor of blood tests. (See Margaret Graham Tebo, New Test for DUI Defense, ABA Journal (Feb. 2005).)

Breathalyzer Less Accurate Than Blood Test

The Breathalyzer is less accurate than a blood test. Whereas a blood test actually measures blood alcohol concentration (BAC), the Breathalyzer merely estimates it. In recognition of this fact, South Dakota relies entirely on blood tests.

What the Breathalyzer attempts to measure is the presence of chemicals found in alcohol. But the machine often measures chemicals with molecular structures similar to those found in alcohol. According to Dr. David Hanson, Over 100 compounds can be found in the human breath at any one time, and 70 to 80 percent of them contain [a] methyl group structure and will be incorrectly detected as ethyl alcohol. (See David Hanson, Ph.D., Breath Analyzer Accuracy, at As a result, false positives can occur for a plethora of reasons.

Causes of False Positive Breathalyzer Tests

Body chemistry is one factor that can lead to false positives. People with diabetes, acid reflux disease, or some cancers can fail Breathalyzer tests even if their bloodstreams are perfectly free of alcohol. Diabetics, for example, have extraordinarily high levels of acetone, a substance that some breath machines mistake for ethyl alcohol.

Police recognize that regurgitation can render unreliable the results of a Breathalyzer. Thus, most departments require that the arresting officer observe the subject of a breath test for twenty minutes before its administration. Regurgitation includes any instance of fluids or gases that rise through the esophagus.

Breath Test Ruled Inadmissible in Court

In 2004, the Illinois Supreme Court ruled inadmissible the results of a breath test where the defendant presented evidence of gastroesophageal reflux disease (GERD). In People v. Bonutti, 817 N.E.2d 489 (Ill. 2004), the defendant had blown a BAC of 0.174 after being stopped and showing outward signs of intoxication. Defendants motion to suppress the Breathalyzer evidence was granted because the court found that the results could have been compromised by a silent, unobservable episode of reflux.

Non-alcoholic substances that people commonly ingest can register on the Breathalyzer. Smokers are often told to wait after consuming a cigarette because chemicals in the smoke can trick the machine. See, e.g., Ind. Admin. Code, tit. 260, r. 1.1-4-8 (providing that the subject of a Breathalyzer test must not smoke within 20 minutes prior to the time a breath sample is taken.) Some non-intoxicating, over-the-counter medications can do the same thing. Even various types of breads can account for BAC levels up to 0.05.

The Breathalyzer is also susceptible to error caused by environmental factors. If a driver has recently pumped gasoline, the alcohol in the fuel can remain on the drivers hands or clothes and can waft into the machine. Compounds that contain the methyl group structure appear in everyday chemicals, such as those found in paints, paint removers, and cleaners. Even electrical interference from cell phones and police radios can disturb the machine.

Women Face Higher Risk of False Positive Breath Tests

Women tend to be at a higher risk of registering a false positive than men. Some breath analysis machines presume a specified hematocrit, which is the percentage of whole blood that is composed of red blood cells. Men naturally have higher hematocrit values than women, but the machines do not adjust according to the sex of the subject. A person with lower hematocrit might have an artificially high BAC reading. Thus, women as a class are in jeopardy of this kind of error. (Hematocrit values can also fall due to blood loss; so, a person tested after being in an accident can register a false positive, adding insult to injury.)

Breathalyzers as Court Evidence

Portable Breathalyzers, which are utilized at traffic stops, are even less reliable than their stationary counterparts. In most jurisdictions, the results from a portable Breathalyzer machine merely provide probable cause to arrest drivers. These machines are susceptible to inaccuracy for reasons as simple as the administering officers improper calibration or carbon monoxide emissions from passing cars. But states are increasingly allowing those results to be used as evidence at trial.

Traditionally, defending a DUI case consisted of attacking the arresting officers probable cause, the officers training in recognizing intoxication, and the polices chain of custody for physical evidence. But as the state relies increasingly on technology to prove its cases, defense attorneys must stay a step ahead in their understanding of the equipment and its shortcomings.

Likewise, a criminal defendant should not concede the accuracy of a Breathalyzer but should hire an attorney who has the time and energy to ensure that dubious test results do not become evidence at trial.

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