Blood ketones test
Quick answer: A blood ketone test measures ketones, substances the body makes when it burns fat for energy instead of sugar. Doctors order it to check for diabetic ketoacidosis in people with diabetes, and sometimes during severe vomiting, fasting or illness.
- SampleBlood
- TakesAbout 5 minutes
- Before the testNo special preparation is usually needed.
How the test is done
- 1A staff member checks your name and asks about your diabetes and recent symptoms
- 2The inside of your elbow is cleaned with a swab
- 3A thin needle draws a small amount of blood into a tube
- 4Pressure is applied with cotton and a small plaster is put on
What your results can mean
Reading your report
Normal ranges differ between labs, so compare your result with the range printed on your report and discuss it with your doctor.
If the result is outside the usual range
A high level can be seen with diabetic ketoacidosis, long fasting, prolonged vomiting, heavy alcohol use or a very low-carbohydrate diet. Low or undetectable ketones are expected in most healthy people who have eaten recently.
Who usually has this test
People with diabetes who feel unwell with high sugars, and anyone with severe vomiting, fasting or illness where ketone build-up is a concern.
Risks and aftercare
You may have a small bruise or mild soreness where the needle went in, which usually settles in a day or two.
Names and options
Also called: serum ketones, beta-hydroxybutyrate, ketone bodies
Listed by the hospital as
- KETONE BODIES BLOOD
Questions about this test
What is the difference between a blood ketone test and a urine ketone test?
A blood ketone test usually measures beta-hydroxybutyrate, the main ketone that builds up in diabetic ketoacidosis, and shows the level at that moment. A urine strip shows ketones passed over the previous few hours. Doctors often prefer the blood test when ketoacidosis is a concern.
Can fasting or a keto diet raise blood ketones?
Yes. Fasting, a low-carbohydrate diet and long vomiting can all raise ketones a little, because the body burns more fat. This is different from the much higher levels with acid build-up seen in diabetic ketoacidosis, which your doctor will judge with other tests.
When should a person with diabetes get ketones checked urgently?
Ketones are usually checked when blood sugar stays high and you feel unwell, especially with vomiting, stomach pain, deep or fast breathing or drowsiness. These can be signs of diabetic ketoacidosis, which needs urgent medical care.
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This page explains each test in general terms so you know what to expect. It is not medical advice: your doctor decides which tests you need and what your results mean. Reference ranges differ between laboratories. Updated 4 November 2026.