ketone
Meaning of ketone: Their presence alone says little; what matters is whether the body chose to make them or was driven to it by missing insulin.
Definition of ketone
Ketones, or ketone bodies, are the small fuel molecules the liver builds from fat when glucose is scarce or cannot be used. There are three: acetoacetate, beta-hydroxybutyrate and acetone. Muscle can burn them, and so can the brain after a period of adaptation. Ketone is separately the name of a broad chemical class, which is why the word also appears on industrial solvents.
Why does the body make them at all?
The brain cannot burn fat directly, and the body cannot convert fat into glucose. Left with only those two facts, a person who stopped eating would be in serious trouble within days. Ketone bodies are the workaround. The liver takes fatty acids released from stored fat and converts them into small water-soluble molecules that travel in the blood and cross into the brain, where they substitute for much of its glucose demand. This shift in metabolism happens during fasting, prolonged exercise, illness and very low carbohydrate eating. Insulin restrains it: as long as some insulin is circulating, the release of fat is limited and ketone production stays modest.
How is ketosis different from ketoacidosis?
| Fasting or dietary ketosis | Diabetic ketoacidosis | |
|---|---|---|
| Insulin | Present, holding fat release in check | Effectively absent |
| Ketone level | Mildly raised and self-limiting | Many times higher and still climbing |
| Blood acidity | Normal | Acidic, because ketone bodies are acids |
| How it appears | Often nothing beyond a change in breath odor | Vomiting, deep rapid breathing, dehydration, drowsiness |
The second is a medical emergency and is the reason ketones are checked when diabetes is poorly controlled or during acute illness. A similar state can follow heavy alcohol use with little food.
How are they measured?
Urine strips detect acetoacetate. Blood meters measure beta-hydroxybutyrate, which dominates during ketoacidosis and shifts back to acetoacetate as the person recovers. That difference has a practical consequence: a urine test can understate the problem early and appear to worsen while blood sugar control is actually improving. Acetone is not measured at all but is exhaled, which is what produces the characteristic sweet odor on the breath.
Also known as
Used in a sentence
Urine testing was performed to check for ketones during the evaluation of the patient's elevated blood glucose.
Good to know
A small rise in ketones can occur normally during fasting or low carbohydrate eating, which is a different state from the far larger buildup seen when insulin is lacking, so the degree of elevation is interpreted alongside the clinical picture.