Ketones are three acidic molecules – beta-hydroxybutyrate, acetoacetate, and acetone – that your liver produces by breaking down fat when carbohydrate or insulin is limited. Mild ketone production is normal during fasting, sleep, or a low-carb diet. Dangerously high ketones happen mostly in type 1 diabetes and signal diabetic ketoacidosis, a medical emergency.
What Ketones Are and Where They Come From
When you eat carbohydrates, your body uses glucose for fuel. When carbs are scarce (fasting, low-carb diet, prolonged exercise, untreated diabetes), the liver shifts to breaking down fatty acids. The byproducts of that breakdown are ketones, which muscles, the heart, and even the brain can burn for energy.
The three ketone bodies are:
- Beta-hydroxybutyrate: The most abundant ketone; measured by blood ketone meters.
- Acetoacetate: Detected by urine ketone strips.
- Acetone: A volatile byproduct; exhaled through the lungs and responsible for the fruity breath of DKA.
Nutritional Ketosis vs Diabetic Ketoacidosis
These two conditions share the word “keto” but are very different.
| Feature | Nutritional Ketosis | Diabetic Ketoacidosis (DKA) |
|---|---|---|
| Cause | Low-carb diet, fasting, exercise | Severe insulin deficiency |
| Blood glucose | Normal (70 – 110 mg/dL) | Usually over 250 mg/dL |
| Blood ketones | 0.5 – 3.0 mmol/L | Above 3.0 mmol/L, often 5 – 20 |
| Blood pH | Normal (7.35 – 7.45) | Below 7.30 |
| Insulin production | Present and working | Absent or insufficient |
| Treatment | None needed | Emergency IV fluids + insulin |
The key difference is insulin. In nutritional ketosis, insulin still keeps ketone and blood sugar levels in check. In DKA, insulin is missing, so both glucose and ketones rise unchecked, dropping blood pH.
Ketone Testing Options
Urine Ketone Strips
Inexpensive (about $10 for 100 strips), widely available, and useful for quick at-home checks. You dip a strip briefly in urine and compare the color to a chart. Limitations:
- Detects only acetoacetate, not beta-hydroxybutyrate
- Reflects ketone levels from hours ago, not now
- Hydration affects accuracy
- False negatives early in DKA when beta-hydroxybutyrate dominates
Learn more in our ketones in urine and urine ketones testing guides.
Blood Ketone Meters
Most accurate and the method of choice for people with type 1 diabetes during illness. A fingerstick drop of blood is applied to a special strip (similar to a glucose meter). Measures beta-hydroxybutyrate directly in mmol/L.
Breath Acetone Meters
Painless and reusable. Quantifies exhaled acetone as a proxy for ketone production. Good for ketogenic dieters; less precise than blood for medical decisions.
Normal and Dangerous Ketone Levels
| Blood Beta-Hydroxybutyrate (mmol/L) | Interpretation | Action |
|---|---|---|
| Under 0.6 | Normal | No action |
| 0.6 – 1.5 | Mild ketosis (fasting, keto diet, early DKA) | Check blood sugar; drink fluids; recheck in 2 hours |
| 1.5 – 3.0 | Moderate ketosis – possible early DKA | Call your doctor; follow sick-day plan |
| Above 3.0 | High risk of DKA | Go to emergency room immediately |
| Urine Ketone Strip Reading | Approximate Blood Equivalent | Action |
|---|---|---|
| Negative | Under 0.5 mmol/L | Normal |
| Trace (5 mg/dL) | 0.5 – 1.0 | Hydrate; recheck |
| Small (15 mg/dL) | 1.0 – 1.5 | Call doctor if diabetic |
| Moderate (40 mg/dL) | 1.5 – 3.0 | Contact doctor; sick-day rules |
| Large (80+ mg/dL) | Above 3.0 | Emergency room |
When to Test Ketones
According to the American Diabetes Association, people with diabetes should check ketones when:
- Blood glucose is over 240 mg/dL for two readings in a row
- You are sick with a cold, flu, vomiting, or diarrhea
- You have nausea or abdominal pain
- You miss an insulin dose
- You feel unusually tired, thirsty, or short of breath
- You are pregnant and have diabetes
People on SGLT2 inhibitors (empagliflozin, dapagliflozin) should also test, as these drugs can cause euglycemic DKA (high ketones at normal blood sugars).
Symptoms of High Ketones / DKA
- Fruity or acetone-like breath
- Deep, rapid breathing (Kussmaul respirations)
- Nausea, vomiting, abdominal pain
- Extreme thirst and frequent urination
- Confusion or drowsiness
- Flushed face
- Muscle aches
If these appear alongside high blood sugar, call 911 or go to the nearest emergency department.
Causes of Elevated Ketones
- Prolonged fasting (over 12 hours)
- Ketogenic or very-low-carb diet (under 50g carbs daily)
- Intense or prolonged exercise
- Pregnancy (starvation ketosis)
- Illness (flu, stomach bug, infection)
- Missed insulin doses or failing pump
- New-onset type 1 diabetes
- Alcohol use (alcoholic ketoacidosis)
- SGLT2 inhibitor medications
How to Lower Ketones
According to the NIDDK, for mild ketosis with diabetes:
- Drink plenty of water to flush ketones
- Take prescribed insulin – do not skip doses even if you are not eating
- Check blood glucose every 2 to 4 hours
- Eat small amounts of carbohydrate if your glucose is not too high
- Follow your sick-day plan
- Recheck ketones every 4 hours
Moderate to large ketones with any vomiting, dehydration, or breathing changes require immediate medical attention.
Ketones in Non-Diabetes Contexts
In people without diabetes, high ketones from a ketogenic diet typically peak around 3 to 5 mmol/L and do not drop blood pH because insulin still moderates the response. Nutritional ketosis has been studied for epilepsy, weight loss, and some cognitive conditions. It is safe for most healthy adults but not for pregnant women, children without medical supervision, or people with liver or pancreatic disease.
The Bottom Line
Ketones are fat-derived fuel molecules your liver makes whenever carbohydrate or insulin is low. Mild ketosis is normal and safe; high ketones with diabetes can quickly become an emergency. Test with urine strips or a blood meter, and know when to call for help. For related topics, browse the prediabetes 101 hub.
