You had a few bites of dinner, or maybe nothing but water all day. You had not been drinking. Then an officer pulled you over; you blew into a breath test device, and the number came back higher than it should have been. If you follow a low-carb diet, fast, or have diabetes, you may be wondering if your body played a trick on the machine.
The answer is that it might have. Ketosis and some health conditions can change what is in your breath, and breath testing devices are not perfect. But the science is not settled, and each case depends on the facts. This post explains how ketosis works, how it may affect a breath test, what else can cause a false high reading, and what to do if you think your result is wrong.
How a Breath Test Works
A breath testing device does not measure the alcohol in your blood directly. It measures the alcohol in your breath and uses a formula to estimate your blood alcohol concentration, also called BAC.
That guess rests on a few assumptions:
- The breath sample comes from deep inside your lungs
- Alcohol is the only thing the device is picking up
- The machine was cleaned, calibrated, and kept in good shape
- The person running the test followed the right steps
When any of these assumptions fail, the number on the screen can be higher than your real BAC. This is what people mean by a false positive.
What Ketosis Is and Why It Matters
Your body normally runs on glucose, a sugar that comes from carbohydrates. When you eat very few carbs, or you go a long time without food, your body switches to burning fat. This process is called ketosis, and it makes substances called ketones.
Ketones are not alcohol. But some are close cousins of chemicals the body can turn into other compounds. Acetone is one ketone that leaves the body through the breath. Some research suggests that at moderate levels, ketones can lead to chemical reactions that produce isopropanol, a type of alcohol. Some breath testing devices may read these substances as if they were alcohol.
How much this matters depends on the device. Some machines are better at telling the difference between alcohol and other chemicals, and others are not. Because of this, no one can say that a ketone-related false positive will happen to every person or on every machine.
Who Can Be in Ketosis
Ketosis is not rare. It can happen to people who:
- Follow a low-carb diet such as keto, Paleo, or Atkins
- Fast for long periods or skip meals
- Exercise hard without eating enough
- Have diabetes, especially when blood sugar is high or poorly controlled
- Are ill, and not eating or drinking normally
For people with diabetes, ketones can also be a sign of a serious medical problem. If you ever notice strong fruity breath, nausea, or confusion, get medical help right away. That is a health emergency, not just a legal issue.
The Swedish Case and What It Shows
A case reported in a medical journal described a sober man in Sweden whose breath set off an in-car breathalyzer and locked his ignition. The man followed a strict low-carb diet. The report suggested his diet may have caused a chemical in his breath that the device mistook for alcohol.
One report does not prove that the same thing will happen to everyone. But it shows that the idea is real enough to be studied, and it helps explain why courts and lawyers take the issue seriously.
Diabetes and Breath Tests
People with diabetes may face extra concerns during a traffic stop. A few points to know:
- High blood sugar can lead to ketones, which may show up in the breath
- Low blood sugar can look like drunk driving, with slurred speech, confusion, or poor balance
- An officer may not be able to tell the difference at the roadside
- Medical records can help explain what was going on
If you have diabetes, keep a record of your diagnosis, medicines, and recent blood sugar readings. These records can be used to show why you may have looked or tested a certain way.
Other Causes of a False High Breath Test
Ketosis is only one possible problem. A breath test can also be thrown off by several other things. Looking at the full list can help you see what may have happened in your own case.
Mouth Alcohol
Mouth alcohol is alcohol that sits in your mouth, throat, or upper airway instead of coming from your lungs. It is often cited as the top cause of false positives. It can come from a recent drink, burping, vomiting, reflux, or dental work that traps liquid.
Acid Reflux and GERD
Reflux can push stomach contents and vapors up into your throat. If this happens close to the test, it can add alcohol that did not come from your lungs. Burping and nausea can have the same effect.
Mouthwash, Breath Sprays, and Other Products
Many mouthwashes, breath sprays, cough syrups, and cold medicines contain alcohol. If you use one shortly before a test, it can raise your reading for a short time.
Chemicals and Fumes
Fumes from paint, solvents, gasoline, and cleaning products may interfere with some breath testing sensors. People who work around these products should mention it.
Calibration, Maintenance, and Software
Breath machines need regular checks. Missed calibration, poor upkeep, or software errors can make a device less reliable. Records can show whether the machine was in good shape.
Operator Error
The person giving the test can make mistakes. Skipping the observation period, testing too soon after you ate or vomited, giving poor instructions, or mishandling the mouthpiece can all change the result.
Breathing Patterns
How you breathe can alter a reading. Hyperventilating may lower it, and holding your breath may raise it. Stress can change the way people breathe, too. These effects can differ from person to person.
Timing and Rising BAC
A breath test shows your BAC at one moment. If the test happens long after you were driving, your BAC may have been different on the road. If you had a drink shortly before driving, your BAC could still have been rising, so a later test may look higher than it was.
What Happens If You Get a False Positive
A false positive can lead to real trouble, even before a case goes to court.
- An officer may arrest you for DUI based on a reading
- A portable roadside breath test can be used to make an arrest, though it generally cannot be used against you at trial
- Your driver’s license may be suspended through an administrative process
- You may be required to use an ignition interlock device
- You may face criminal charges and penalties if the case moves forward
Georgia has administrative license suspension rules, and deadlines can be short. Even if you plan to fight the charge, you should not ignore license deadlines.
Evidence That Can Challenge a Breath Test Result
If you think ketosis, diabetes, or another factor caused a false reading, certain evidence can help show it.
- Medical records that show a diagnosis, such as diabetes
- Records of your diet or fasting before the stop
- Video from the officer’s body camera or dash camera
- Witness statements about your behavior before the stop
- The printout from the breath test machine
- Calibration and maintenance records for the device
- The operator’s notes and training records
- Analysis from an expert, such as a toxicologist
An independent blood test can also be useful. After the state’s test, you may be able to request additional testing from a medical professional of your choice, usually at your own cost. Ask clearly and quickly, and write down what happens if the request is refused.
What to Do If You Think Your Breath Test Was Wrong
What you do after the stop matters. Keep these three steps in mind.
Write Down the Details Right Away
Memory fades fast. Write down everything you can recall, such as:
- What you ate and drank, and when
- Whether you were following a low-carb diet or fasting
- Any medicine you took, including diabetes medicine
- Any health conditions
- Any burping, reflux, nausea, or vomiting
- How the officer acted and how the test was given
- The time between the stop and the test
Do Not Explain Yourself to Police Afterward
Talking to police after the fact can hurt you. Guesses and half-memories can be used against you later. Share your notes with your attorney, not with the officer.
Talk to a DUI Defense Attorney Early
An attorney can ask for video, machine records, and maintenance logs before they are lost. The sooner you call, the better the chance of keeping the evidence you need.
Frequently Asked Questions
Can a low-carb or keto diet cause a false positive breath test?
It may. Ketosis can raise ketones in your breath, and some devices may read them as alcohol. The effect depends on the device and the person, and the science is still debated, so each case needs to be looked at on its facts.
Can diabetes cause a high breath test reading?
Diabetes can lead to ketones, especially when blood sugar is high, and those may show up in the breath. Low blood sugar can also cause symptoms that look like drunk driving. Medical records can help explain what was happening.
Does fasting or skipping meals affect a breath test?
It can lead to ketosis, which may affect some breath tests. Tell your attorney if you were fasting or had gone a long time without eating.
Can I be arrested based on a roadside breath test?
Yes. A portable breath test can be used by an officer to make an arrest, even though it generally cannot be used against you at trial. That is why a false positive can still cause serious problems.
What should I do if I think ketosis or diabetes affected my test?
Write down the details, keep your medical and diet records, avoid explaining yourself to police, and speak with a DUI defense attorney as soon as you can. Ask about an independent blood test as soon as possible.
Talk to a Savannah DUI Attorney About Your Breath Test
A high breath test reading does not always mean what the officer says it does. Ketosis, diabetes, mouth alcohol, device problems, and other issues can lead to a number that does not match your real BAC. Every case is different, and the right steps depend on the facts of your stop and your test. Jarrett Maillet J.D., PC, can review what happened, look at the evidence, and explain your options. Call 912-713-3426 for a free consultation to talk about your case.
