Understanding the Ketogenic State
Ketosis is a metabolic process that occurs when the body, deprived of carbohydrates, switches its primary energy source from glucose to fat. To utilize fat for fuel, the liver breaks it down into chemical compounds called ketones. While a normal metabolic process, the production of these ketones has a direct and significant impact on breath test results for alcohol.
Ketones and Acetone
Three main types of ketone bodies are produced during ketosis: acetoacetate, beta-hydroxybutyrate, and acetone. Acetone is a volatile compound, meaning it can evaporate and be exhaled from the lungs, which is why individuals in ketosis often have a distinct, fruity or metallic-smelling breath. It is this exhaled acetone that can interfere with certain breathalyzer devices.
The Problem with Less Sophisticated Breathalyzers
Most roadside breathalyzers, which use electrochemical fuel cell technology, are designed to measure the amount of ethyl alcohol (ethanol) on a person's breath. Unfortunately, some of these devices are not sophisticated enough to distinguish between ethanol and other alcohols, such as the isopropyl alcohol that is chemically similar to acetone. The result is that a breathalyzer test can register the presence of acetone as if it were ethanol, potentially leading to a false positive result and an inaccurate blood alcohol concentration (BAC) reading.
The Impact on Drivers
The consequences of a false positive can be severe. An officer administering a roadside test may have their suspicion confirmed by a reading, even if the person has not consumed alcohol. This can lead to an arrest and the need for further, more accurate testing at a police station. Even a low false BAC reading can be problematic, as it could potentially trigger an ignition interlock device in a vehicle required for a past offense. In combination with small amounts of actual alcohol, the ketone reading could push an individual over the legal limit.
How Different Breathalyzers are Affected
Not all breathalyzer devices are created equal when it comes to detecting ketones. Law enforcement typically relies on different technologies for roadside screening versus evidentiary testing at the station.
| Device Type | Technology | Susceptibility to Ketone Interference | Reliability | Used For |
|---|---|---|---|---|
| Roadside/Portable Breathalyzer | Electrochemical Fuel Cell | High: Can mistake acetone for ethanol. | Lower, used for probable cause. | Initial traffic stop screenings. |
| Evidentiary Breathalyzer | Infrared Spectroscopy (IR) | Low: Can differentiate between acetone and ethanol based on molecular structure. | Higher, used for evidence in court. | Official BAC testing at police stations. |
| Blood Test | Laboratory Analysis | Zero: Measures actual blood alcohol, not breath compounds. | Highest, most definitive. | Confirmatory testing for DUI arrests. |
The Legal Lifeline: Blood Tests
The key takeaway for anyone concerned about a false positive is the reliability of a blood test. A blood sample is sent to a laboratory where it is analyzed to determine the actual presence and concentration of ethanol. This test is definitive and will not produce a false positive due to ketones from ketosis. If you are ever faced with a DUI arrest after a breathalyzer reading while in ketosis, requesting a blood test at the station is your best course of action to prove your sobriety.
Ketosis vs. Diabetic Ketoacidosis (DKA)
It is crucial to distinguish between nutritional ketosis, which is generally benign, and diabetic ketoacidosis (DKA), a dangerous and life-threatening medical emergency. In DKA, ketone levels are dangerously high due to a severe lack of insulin in a person with diabetes. Symptoms of DKA can include confusion, flushed face, and a very strong, fruity breath odor that mimics alcohol intoxication and will almost certainly produce a false positive on a breathalyzer. If you have diabetes and notice these symptoms, seek immediate medical attention, as DKA is a medical crisis, not a simple dietary effect.
Steps to Take if You're Concerned
If you are on a low-carb or ketogenic diet, or have a medical condition like diabetes, it's wise to be prepared. Here are some steps you can take:
- Maintain Medical Records: If you have diabetes, keep a medical history readily available that documents your condition. A physician's letter confirming a state of therapeutic ketosis can also be valuable.
- Stay Hydrated: Drinking plenty of water can help flush out ketones and may slightly dilute the acetone in your breath.
- Request a Blood Test: After a roadside breathalyzer reading, immediately and clearly request a blood test to confirm your BAC.
- Understand Your Legal Rights: In a DUI situation, it is important to exercise your right to legal counsel. A knowledgeable attorney can use the evidence of your ketosis to challenge the breath test results.
- Distinguish Between Tests: Recognize that the initial test at a traffic stop is different from the more accurate, evidentiary test at the police station. Be prepared for the possibility of a false roadside reading.
Conclusion: The Bottom Line on Ketosis and Breathalyzers
While the science confirms that ketosis can produce false-positive readings on less sophisticated breathalyzer devices, particularly roadside versions, it does not mean you will inevitably fail an evidentiary test. The key is to understand the different technologies and procedures involved. For those following a keto diet or managing diabetes, awareness is the best defense. The ability of more advanced tests, like infrared breathalyzers and confirmatory blood tests, to differentiate between ketones and true alcohol provides a clear path to resolving any inaccurate initial readings. Remember, a false positive on a breathalyzer is a possibility, but with the right steps, you can protect yourself from wrongful charges.
For more information on the production and testing of ketones, you can visit the Cleveland Clinic website.
