When and Why to Measure

Ketones are molecules produced by the liver when the body shifts from using glucose to using fat as its primary fuel source.¹ This process, known as ketosis, occurs during prolonged fasting, carbohydrate restriction, extended exercise, or insulin deficiency.

The main circulating ketone measured in blood is beta-hydroxybutyrate (BHB).² Under normal conditions, ketone levels are low (<0.5 mmol/L). During nutritional ketosis—such as with a ketogenic diet—BHB levels typically range from 0.5–3.0 mmol/L.³ This differs significantly from diabetic ketoacidosis (DKA), a serious condition characterized by very high ketone levels, hyperglycemia, and metabolic acidosis.⁴

When Should Blood Ketones Be Measured?

1. During Illness in Type 1 Diabetes
The American Diabetes Association recommends checking ketones when blood glucose is persistently elevated (≥250 mg/dL) or during illness.⁴ Early detection of rising ketones can help prevent DKA.

2. While Following a Ketogenic Diet
Individuals using carbohydrate restriction for metabolic or weight management may measure ketones to confirm they are in nutritional ketosis. Blood ketone testing provides a more accurate reflection of current ketone status than urine testing.²

3. During Prolonged Fasting
Ketone production naturally increases during fasting as the body shifts to fat metabolism.¹ Monitoring may provide insight into metabolic flexibility, though routine testing is not necessary for most healthy individuals.

Why Use Blood Ketone Testing?

Blood testing measures beta-hydroxybutyrate directly and detects ketosis earlier and more accurately than urine strips, which measure acetoacetate and can be affected by hydration status.²

Blood ketone measurement is a useful tool in specific situations—particularly for people with type 1 diabetes during illness or for those intentionally following a ketogenic diet. As with any metabolic marker, ketone levels should be interpreted alongside blood glucose levels and clinical symptoms.

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The content of this article is intended to provide a general information and knowledge on the subject matter. The views expressed in newsletters, articles, and blogs in the i-SENS USA website are not necessarily those of i-SENS Incorporated, i-SENS USA Incorporated or our publishers. Medical or nutritional information on i-SENS USA website is not intended to replace professional medical advice – you should always consult a specialist with any questions about your specific circumstances.