Causes of Breathalyer False Positives

July 22, 2019

A breathalyzer is an essential tool in roadside alcohol tests. The concept is simple. You blow into the device, and it tests your blood alcohol content (BAC). If you breathe over the limit, 0.08 in Ontario, you’re facing a criminal offence. However, there are several factors that can cause false positives in breathalyzer tests.

Health Conditions

Some health conditions can make it possible to test positive for blood alcohol regardless of whether you’ve had a drink.

Acetone, for instance, can cause a false positive on a breathalyzer test. It is a compound that your body produces naturally. A diabetic with hypoglycemia can blow a BCA of 0.06.

Although that’s lower than the 0.08 limit, it’s still enough to potentially have your license suspended. And combined with even one drink, that can easily put you over the limit.

Acid reflux can also cause a false reading. As well as gastrointestinal disease and heartburn.


Your eating habits can have a direct impact on the outcome of a roadside stop. Even a health-conscious diet won’t prevent you from blowing a false positive during a roadside stop.

Some of the most popular diets, from Atkins to Keto, focus on reducing or eliminating carbs. A low-carb diet can result in higher acetone levels. So as with hypoglycemia, a low-carb diet can cause you to show a higher BAC on breath tests.

There are also a number of specific foods that can cause a false positive. Today, many professionals are skipping out on breakfast, grabbing a protein bar to eat in their car instead. But this breakfast-to-go could get you to test positive on alcohol screening tests.

Here are a few of the foods that can fail a breathalyzer test:

  • Protein bars
  • Nuts
  • Bread
  • Energy Drinks
  • Ripe Fruits
  • Sugarless gum

One of the causes of this is that many foods use a fermentation process as a preservative. And even though this fermentation won’t result in a buzz, a breathalyzer can’t make the distinction. In ripe fruits, this fermentation occurs naturally.

If you test positive for drunk driving, be sure to let your drunk driving defence lawyer know what you ate that may have attributed to the result.

CBD or THC will not cause a Breathalyzer False Positive reading.

Improper Device Calibration

One of the most common defences in DUI cases is challenging device calibration. A breathalyzer should be carefully maintained and re-calibrated frequently. If the police do not keep up-to-date with the calibration schedule, there is a higher probability of a false reading.

As well, the device needs to be calibrated for the situation. For instance, most breath screening devices are sensitive to temperature. Failing to adjust the device for the temperature can result in a false reading.

The device has to fall under a list of accepted devices. Some widely used breathalyzers have been deemed too inaccurate to rely on in Ontario courts.

Improper Administration

Without the proper administration of alcohol screening tests, police cannot accurately gauge BAC. A breathalyzer operates under the assumption that the breath is coming from deep in the lungs, so if there is alcohol in the mouth it will display a higher blood alcohol concentration.

To prevent mouth alcohol from causing a false positive, the officer is supposed to keep you under observation for 15-20 minutes before administering the test. Even a small amount of alcohol in the mouth or throat can severely impact results.

Additionally, burping, vomiting, and acid reflux reset the clock on administering a test. These can move alcohol from the stomach into the mouth, causing the same mouth alcohol issue. So, after an instance of burping or vomiting officers are supposed to wait another 15 minutes before testing.

Drunk Driving Defence Lawyer

While testing positive on a breathalyzer test can have immediate consequences, it doesn’t mean you’ll be convicted. If you face charges for driving under the influence, contact a Toronto DUI attorney as soon as possible. They will help you understand your charges, your options, and the possible outcomes.

William Jaksa is a Toronto criminal defence lawyer with expertise and experience in handling DUI offences. Contact us today for a consultation.

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