It's many people's worst nightmare. You're driving after having had a drink or two--or maybe no drinks at all--and are pulled over. You honestly don't feel "under the influence" in the slightest. But your performance on your field sobriety tests makes an officer suspicious, you are arrested for DUI---and a DUI breath test or blood test shows that you have a BAC of 0.08 or above.
This doesn't have to be the end of the story. Inaccurate DUI chemical test results are actually among the top 10 legal defenses to California DUI charges.
The phenomenon of "residual mouth alcohol" is one reason why DUI breath test results might show an artificially inflated BAC. This is especially common for people who have gastroesophageal reflux disease (GERD). Basically, if you burp, belch, or regurgitate prior to a DUI breath test, alcohol in the mouth will mix with alcohol from your lungs and make your BAC look much higher than it actually is.
Another medical situation that can lead to artificially high BAC measurements on DUI chemical tests is "ketosis." Ketosis is common in people with diabetes or hypoglycemia, people who have been fasting, and people who follow low-carbohydrate high-protein diets like Atkins or Paleo. Ketones are a chemical substance released into the breath that can be mistaken by a breath test for the alcohol produced by drinking.
The bottom line is: chemical tests for DUI are not foolproof or infallible! Even when correctly administered, they can produce falsely high BAC results, particularly in people who
- have GERD,
- have diabetes or hypoglycemia, or
- are on a low-carb or fasting diet.