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What are some Causes of False Positives for DUI Breathalyzer Tests

We have all been there with that unsettling feeling that you get when you see the flashing lights in your rearview mirror and hear a patrol car’s siren coming upon you. However, what happens next can be life changing. If that officer asks you to take a breathalyzer test, the results can have a monumental effect on your life, liberty and freedom. Failing a breathalyzer test means that you are over the legal limit for your blood alcohol content (BAC) and criminal prosecution will ensue. The following talks about the accuracy of breathalyzer tests and your defense against these seemingly infallible results.

What is a false positive breathalyzer test?

While most prosecutors and law enforcement officials would have you believe that the results of a breathalyzer test are infallible, that is a bit of a stretch on the truth. Generally, breathalyzer tests are only accurate approximately 40% of the time. Factor into that statistic that the testing equipment itself has an inherent margin of error between .005 and .02% in its BAC readings. Taken into consideration, these various characteristics can lead to a false positive reading by a breathalyzer test. That false positive reading means that you will be charged with driving under the influence (DUI), a very serious crime which can have wide ranging implications on your daily life.

Appropriate and qualified administration of a breathalyzer test

The appropriateness and administration of a breathalyzer test is a very important factor in determining what your true BAC actually is. In terms of appropriateness, timing makes all the difference. One instance of timing making a difference is with your blood alcohol being “on the rise.” This rising occurs because it can take anywhere between fifty (50) minutes to three (3) hours for your system to fully absorb any alcohol that you may have imbibed. Thus, your blood alcohol level could have been within the legal limit while driving, but between the time you were stopped and the test administered, your BAC could have risen just enough to put you over the legal limit.


Another instance where timing makes a difference is in how the test is administered. First, police must wait a minimum of fifteen (15) minutes before administering a breathalyzer test. This time is necessary to prevent any alcohol in the mouth cavity from being registered by the test because the test is only supposed to measure alcohol from deep within the lungs. Additionally, if you take a drink, burp, pick up or vomit during this waiting period, the clock has to start all over with a new fifteen (15) minute period. Otherwise, the breathalyzer test will yield a false positive result.

In terms of qualified administration, there are two (2) main areas which could yield a false positive result. The first area is whether the test machine was improperly calibrated. Improperly calibrated equipment produces improper results. There have been numerous cases about improperly calibrated equipment being used in DUI prosecutions and convictions. Recently, the state of New Jersey had to overturn thousands of DUI cases due to improperly calibrated equipment.

The second area of qualification has to do with the officer administering the test itself. Not just anyone can administer a breathalyzer test. The officer conducting the test has to be specially trained in use of the breathalyzer equipment. Otherwise, failure to properly operate the test equipment can mean a false positive result.

Ingested substances and BAC

Ingested foreign substances, whether via drinking, eating, injected or by other means, can impact BAC reading levels. Even if the ingested substance does not contain alcohol, the test equipment readings may be impacted. For instance, being on a low-carb diet makes your body burn stored fat for energy, and by doing so, your body produces ketones and acetones. While this is great for losing weight, the acetones can get carried on your breath and cause a higher BAC test reading. Oddly enough, even fasting (i.e., not ingesting or eating anything) can cause this same phenomenon and the same abnormally high BAC reading.


Medication and its impact on a breathalyzer test

Can medications impact breathalyzer test results? The answer is a resounding ‘yes!’ Many medications impact the blood stream. Additionally, when a medication is administered multiple times a day, particularly if administered with an inhaler, then a breathalyzer test can register an erroneous BAC level. A frequent example of the medication impact occurring is with asthma inhalers. Most inhalers contain compounds that act similarly to the ethanol alcohol found in an alcoholic beverage.

Man taking prescription medicine
Prescription medication can affect blood alcohol levels

Medication have an affect on BAC readings is particularly true with the commonly prescribed Albuterol asthma medicine. Albuterol contains methyl compounds that have been shown to give false positive readings registering as high as .21 BAC. The acid produced in the stomach or esophagus from heartburn, acid reflux and gastrointestinal reflux disease can skew a breathalyzer test as well. Even breathing into the breathalyzer equipment with short breaths can produce inaccurate readings, leading to you unjustly being charged with a DUI.

The wide-spread question, “can diabetes give false BAC readings?” has also been a topic for DUI defense. The short-answer is yes, however, it is best to speak with an attorney to help guide you through all of the scenarios where diabetes can affect these readings.

What Environmental Factors can Impact Positive DUI Test Results?

Many environmental factors can impact a test reading. Even airborne factors, as opposed to ingested ones, can affect the test readings. The following are some of the common instances of environmental contaminants that have negatively impacted breathalyzer test readings before:

  • paint fumes and solvents,
  • the alcohol in cleaning supplies,
  • chemicals associated with adhesives and plastics,
  • the alcohol fumes from the previous person tested by the same machine,
  • rubbing alcohol fumes and remnants on the skin,
  • dust particles from deployed vehicle safety airbags (also known as the Tyndall (scattering) effect),
  • whether the breathalyzer test equipment’s software is up-to-date,
  • the ‘freshness’ and type of battery in the breathalyzer equipment,
  • any contaminants still present in the testing mouthpiece (e.g., usually occurs when the test administrator fails to change the mouthpiece before administering a new test), and
  • many others.

Other Factors Impacting the Accuracy of a Breathalyzer Test

The breathalyzer equipment is a highly sensitive piece of machinery. While important in its use, due to its high level of sensitivity, it can be made to offer erroneous readings due to even common foods (such as a sweet honey bun snack), drinks (non-alcoholic in nature), and other household items. Some of the foods, drinks, and other household items that have caused previous false positive readings appear below:


  • honey buns or glazed cinnamon rolls,
  • ripe or fermented fruit,
  • sugarless gums,
  • breads (especially white or sourdough),
  • protein bars,
  • hot sauces, and
  • foods prepared or cooked with alcohol (i.e., beer, liquor, or wine)


  • non-alcoholic beer or wine,
  • energy drinks, and
  • fermented sodas

Other Household Items:

  • over-the-counter medicines, such as sleep aids or cough syrup,
  • certain vitamins,
  • mouthwashes containing alcohol,
  • breath fresheners (particularly breath sprays),
  • scented products used around the mouth, such as after-shave ointments or cosmetics, and
  • denture creams/adhesives.


Any attorney seeking to defend you against a DUI charge will use a combination of the applicable Arizona law, with statutes and relevant case law, to offer the best defense possible. Aggressive challenging of any DUI charge means defending you against inaccurate false positives. This defense includes being able to question the person who administered the test. This person needs to be at the trial, otherwise that denies your constitutional right to confront your accuser. Having an attorney experienced in DUI crimes is key to maintaining your good name and liberty.

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