Ketones in the Urine
Ketones in the urine usually mean the body has been running on fat, as it does during fasting, illness, vomiting, or a low-carbohydrate diet. On its own, with a normal glucose, that is ordinary metabolism and not a warning. The one situation that overturns this is SGLT2 inhibitor treatment, where ketoacidosis can develop with a glucose that looks close to normal — so the glucose reading cannot be used to rule it out.
The pattern on your report
- Ketones High Key
- Glucose Normal Key
- Bicarbonate Normal Key
- Urine glucose Normal Key
Printed as: Bicarbonate in mmol/Lor mEq/L— Labeled total CO2 on some panels. This is the value that separates ketosis from ketoacidosis.Glucose in mmol/Lor mg/dL— Places the finding in almost everyone, but it cannot exclude ketoacidosis in someone on an SGLT2 inhibitor.Urine glucose in dipstick grade— Positive by design in anyone taking an SGLT2 inhibitor, so it carries no information in that group.Ketones in dipstick grade— Detects mainly acetoacetate, while the ketone that predominates in severe illness is a different one, so it can understate an episode.
Why the numbers look like this
When glucose is unavailable or cannot get into cells, the liver breaks down fat and produces ketones as an alternative fuel. The brain uses them, and the process is a designed adaptation to going without food.
What makes ketones dangerous is not their presence but their quantity and the acid they carry. In diabetic ketoacidosis, a near-total absence of insulin removes the brake on fat breakdown entirely, so ketones accumulate far beyond what fasting produces and the blood turns acidic.
SGLT2 inhibitors change the picture in a way that catches people out. They cause glucose to be lost in the urine, which lowers the blood glucose and reduces insulin secretion, which in turn releases the brake on fat breakdown. Ketoacidosis can therefore develop while the glucose sits near its usual range, and the illness is fully as dangerous as the classic version.
One more mechanism deserves a mention. The urine strip detects mainly one ketone, acetoacetate, while the ketone that predominates in severe illness is a different one. So during a severe episode the urine test can understate the problem, and it can also appear to worsen during recovery as one ketone converts to the other.
Not being flagged is not the same as normal
The urine strip reports what the kidney has been discharging over the preceding hours, not what is in the blood now, so it lags and cannot be used to follow an evolving situation. Blood ketone measurement, on a meter that reads the predominant ketone directly, is used for monitoring for that reason. A trace of ketones in a well person who has skipped meals is unremarkable and needs nothing.
What else on the report can hide this
Glucose alongside places this immediately in most cases. Ketones with a normal glucose in a well person who has been fasting or eating few carbohydrates needs no action.
The critical exception is anyone taking an SGLT2 inhibitor, where a normal glucose does not exclude ketoacidosis. In that situation symptoms decide: nausea, vomiting, abdominal pain, rapid breathing or feeling profoundly unwell warrant urgent assessment regardless of what the glucose says.
Bicarbonate is the value that shows whether acid is accumulating, and a low bicarbonate with ketones is a different situation from ketones alone.
In pregnancy the finding carries more weight, since ketosis develops faster with the fasting of severe morning sickness and matters more.
In a child, ketones with vomiting deserve a lower threshold for assessment, because children move from ketosis to ketoacidosis faster than adults do and dehydrate more readily.
What usually causes it
Listed from most to least common — not from most to least serious.
- Very common
Fasting or skipped meals
The commonest reason by far, including an overnight fast before the test. A trace in a well person needs nothing.
- Very common
A low-carbohydrate or ketogenic diet
Deliberate and expected. The glucose is normal, the bicarbonate is normal, and the person is well.
- Very common
Vomiting or a diarrheal illness
Reduced intake with increased demand. Resolves as the illness does and as eating restarts.
- Common
Alcohol with poor intake
Can produce a genuine ketoacidosis with a glucose that is normal or low. Suspected from the history rather than the numbers.
- Common
Diabetic ketoacidosis — in people with diabetes
Ketones with a high glucose, a low bicarbonate, thirst, vomiting and rapid breathing. A medical emergency.
- Uncommon
Ketoacidosis on an SGLT2 inhibitor
The same emergency with a glucose that looks close to normal. The glucose reading cannot be used to exclude it.
- Uncommon
Pregnancy with reduced intake — in people who are pregnant
Ketosis develops faster and matters more, particularly with severe morning sickness.
- Uncommon
Prolonged intense exercise
Transient and benign in a well person eating normally afterwards.
- Rare
An inherited metabolic disorder — in infants and young children
Recurrent episodes with illness, sometimes with low glucose. A specialist diagnosis.
What is usually checked next
- Blood glucose alongside Places the finding immediately in almost everyone, with the single exception below.
- Ask about SGLT2 inhibitor treatment The one situation where a normal glucose does not exclude ketoacidosis, and it changes the assessment.
- Bicarbonate Shows whether acid is accumulating, which is what separates ketosis from ketoacidosis.
- Blood ketone measurement if the situation is evolving The urine strip lags and reads a different ketone, so it cannot be used to follow an episode.
- A symptom review Nausea, vomiting, abdominal pain or rapid breathing outweigh any reassuring number.
When to seek care sooner
- Emergency Vomiting with abdominal pain and rapid or deep breathing
- Emergency Drowsiness or confusion
- Emergency Feeling profoundly unwell while taking an SGLT2 inhibitor
- Emergency Ketones with a high glucose and excessive thirst
- Same day A child with ketones who is vomiting
- Same day Persistent vomiting in pregnancy
Questions worth bringing to your appointment
- Had I eaten before this test?
- Am I on any medicine that makes me lose glucose in my urine?
- Was my bicarbonate normal?
- Do I need a blood ketone measurement rather than a urine one?
- What symptoms should make me seek help urgently?