What Do Blood Ketone Readings Mean?

Ketones are fuels your liver makes from fat when there’s little carbohydrate or insulin to go around: during fasting, on a very low-carbohydrate diet, after long exercise, and, dangerously, in uncontrolled diabetes. Home ketone meters measure the main one, beta-hydroxybutyrate (BHB), in a drop of blood from your finger, in millimoles per litre (mmol/L). The same number can be expected on a ketogenic diet and an emergency in someone with type 1 diabetes, so what a reading means depends on who you are.

This article is general information, not medical advice. If you have diabetes, follow your care team’s sick-day plan for ketones.

Typical Levels

BHB (mmol/L)	Typical situation
Under 0.5	After an ordinary mixed diet
0.5 to 3.0	Fasting for a day or more, or a ketogenic diet; often called nutritional ketosis
Several mmol/L	Prolonged fasting over days to weeks
3.0 or more, with high glucose or diabetes	Diabetic ketoacidosis, an emergency

The “nutritional ketosis” range is a convention from ketogenic diet research, not a clinical guideline. In his review of fuel metabolism in starvation, Cahill describes how ketones rise steadily over days of fasting as the brain shifts to using them, reaching levels well above those of a ketogenic diet.

When Ketones Are an Emergency

Diabetic ketoacidosis (DKA) happens when there’s too little insulin: the body breaks down fat uncontrollably, ketones build up, and the blood becomes acidic. It’s most common in type 1 diabetes and can be fatal. The 2024 international consensus report on hyperglycaemic crises, from the American Diabetes Association and other societies, diagnoses DKA when all three are present:

• Glucose of 200 mg/dL (11.1 mmol/L) or more, or a known history of diabetes.
• BHB of 3.0 mmol/L or more (or urine ketones of 2+ or more).
• Acidosis: a pH under 7.3 or bicarbonate under 18 mmol/L, measured in a blood test.

The glucose criterion no longer requires a very high value, because DKA can happen with near-normal glucose, notably in people taking SGLT2 inhibitor medicines for diabetes. In people without diabetes, a high reading from fasting is usually not acidosis, since enough insulin keeps ketones in check.

Get urgent medical care for high ketones with nausea, vomiting, abdominal pain, fast breathing, confusion, or unusual drowsiness, whether or not you have diabetes.

Getting Reliable Readings

• Use blood, not urine or breath, for a number you can compare. Urine strips show ketones you’ve excreted, and change with how much you drink.
• Wash and dry your hands first, and use the meter’s own strips within their date.
• Measure at the same time of day, since ketones are usually highest in the morning after an overnight fast and lower after meals.

Following It in Kaizora

Capillary Blood Beta-Hydroxybutyrate is on the Vitals page; log each reading in mmol/L. On Correlations, putting it beside Dietary Total Carbohydrate or Dietary Net Carbohydrate by day shows how your ketones follow what you eat. Add your own reference range for the band you aim for, or a severe one at 3.0 mmol/L if you have diabetes; see Reference Ranges.

The Short Version

• Home meters measure beta-hydroxybutyrate, the main ketone, in mmol/L.
• 0.5 to 3.0 mmol/L is typical of fasting or a ketogenic diet.
• 3.0 mmol/L or more with diabetes or high glucose can mean ketoacidosis, an emergency.

Sources

• Umpierrez GE et al., “Hyperglycemic crises in adults with diabetes: a consensus report,” Diabetes Care 47, no. 8 (2024): 1257–1275. doi:10.2337/dci24-0032. Free full text.
• Cahill GF, “Fuel metabolism in starvation,” Annual Review of Nutrition 26 (2006): 1–22. doi:10.1146/annurev.nutr.26.061505.111258