Ketones in urine: what they mean and the normal result

Ketones in urine, or ketonuria, are a sign that the body is burning fat for fuel instead of glucose. A urine test reports them as negative, or as trace, small, moderate or large. Small amounts are common after fasting, on low-carbohydrate diets and during illness. In someone with diabetes, larger amounts can be an early warning of ketoacidosis, which needs prompt medical care.

What it measures

When cells cannot get enough glucose, either because little carbohydrate is coming in or because there is not enough insulin to use it, the body breaks down fat. The liver turns the fatty acids into ketone bodies: acetoacetate, beta-hydroxybutyrate and acetone, which forms as acetoacetate breaks down. They are a normal back-up fuel that many organs can use, which spares glucose for the brain. The excess leaves the body in urine and, as acetone, in the breath.

The urine strip uses a nitroprusside reaction. It detects acetoacetate but not beta-hydroxybutyrate, the main ketone in the blood during diabetic ketoacidosis. So urine ketones are a useful screen rather than a precise measure, and when precision matters, doctors measure beta-hydroxybutyrate in blood.

Normal range

The normal result is negative. MedlinePlus notes that some ketones in urine can be normal, and that what counts as normal varies with diet and activity.

For adults with diabetes, the 2024 international consensus on hyperglycaemic crises uses these levels:

A blood beta-hydroxybutyrate of 3.0 mmol/L or more matches diabetic ketoacidosis with over 90% sensitivity and specificity, but the diagnosis also needs high glucose or known diabetes, and acid in the blood. Labs and strip makers word their bands differently, and ranges vary by laboratory and method, so read your result against your own report.

What a positive result usually points to

Fasting, diet and exercise

Ketones are expected when carbohydrate is scarce: during fasting or starvation, on a ketogenic or other very low-carbohydrate diet, after prolonged hard exercise, and with prolonged vomiting or diarrhoea. They are also seen in pregnancy, especially with vomiting in early pregnancy, and can appear with high fever, severe illness, an overactive thyroid, heavy alcohol use and eating disorders.

Diabetes

In diabetes, ketones rise when there is not enough insulin to move glucose into cells. If they build up, the blood becomes acidic, which is diabetic ketoacidosis (DKA). It is most associated with type 1 diabetes but can happen in type 2. Early signs include thirst, passing a lot of urine and headache; later ones include nausea or vomiting, abdominal pain, confusion, difficult breathing and fruity-smelling breath. MedlinePlus describes DKA as a medical emergency, so ketones with those symptoms in someone with diabetes are a reason to seek medical help straight away.

SGLT2 inhibitors

These diabetes medicines can lead to ketoacidosis with blood glucose that looks near normal, called euglycaemic DKA, and the 2024 consensus says they now account for most cases of it. Prolonged fasting, very low-carbohydrate diets, dehydration and heavy alcohol use raise the risk. In someone taking one, ketones are read on their own merits rather than dismissed because glucose is normal.

What a doctor typically checks next

• Blood glucose and, where diabetes is known or suspected, blood beta-hydroxybutyrate.
• Bicarbonate in blood, which falls when ketones make the blood acidic.
• HbA1c, for the longer picture of blood sugar.
• Urine glucose from the same sample.
• When you last ate, how much you have been eating, and any vomiting.

What moves it

• Time since eating. Liver glycogen supplies glucose for around 12 hours; after that, ketone production picks up.
• Very low intake. The consensus links starvation ketosis to intake below about 2,090 kJ (500 kcal) a day.
• Exercise. Prolonged intense exercise raises ketones.
• Delay in testing. A sample that is stored badly or tested late can read falsely negative.
• Medicines and the sample itself. Captopril and other drugs with sulfhydryl groups, valproate, levodopa and mesna can cause false positives on the strip, as can very concentrated, acidic or strongly coloured urine.

Preparing for the test

No preparation is needed for the urine strip itself. If blood tests at the same visit ask you to fast, bear in mind that a longer fast can itself produce small amounts of ketones. Note when you last ate, any hard exercise in the day before and any vomiting, and tell the person taking the sample about your medicines, including SGLT2 inhibitors.

How Clare's panel handles it

In Clare's panel, urine ketones are measured by the lab as part of the urine test. They are read alongside urine glucose and, in blood, fasting glucose, HbA1c and bicarbonate. The panel does not include blood beta-hydroxybutyrate, and a routine panel is not the way to assess someone who is unwell: anyone with diabetes, ketones and symptoms of DKA needs urgent medical care.

Why it matters in the UAE

Ramadan is the main local reason ketones show up in healthy people. The IDF and DAR Ramadan guidelines explain that liver glycogen covers about 12 hours, so most people who eat at suhoor have used up their glycogen by late afternoon and start making ketones. Skipping suhoor brings that forward. A urine sample taken late in a fasting day can therefore show ketones for a reason that has nothing to do with illness.

For people with diabetes, the same guidelines list DKA among the risks of fasting, though studies disagree on whether it is more common during Ramadan than in other months. The IDF estimates that about 79,000 people of all ages live with type 1 diabetes in the UAE, the group for whom ketone testing matters most.

Related tests

Urine ketones are read with urine glucose from the same sample, with fasting glucose and HbA1c from the HbA1c and diabetes test, and with bicarbonate from the kidney function test. Our article on reading HbA1c, glucose and insulin together covers the blood side.

Why it means more over time

Ketones change within hours, with meals, fasting and exercise, so a single result mostly tells you about the day of the test. Over time the pattern is what helps: ketones that appear on fasting days or a low-carbohydrate diet fit the way the body normally switches fuel, while ketones alongside rising glucose or HbA1c are worth taking to a doctor. People with type 1 diabetes, and people taking an SGLT2 inhibitor, are usually advised by their doctor to check ketones when they are unwell.

Clare is opening with a waitlist at clare.health.