Ketones in urine: what your result means
Ketones in urine are a common finding on a urine dipstick and in a standard urinalysis. Usually they just mean your body is burning fat for energy. Occasionally they signal a serious problem. This guide explains what trace, small, moderate and large results usually mean, the common causes, the difference between harmless ketosis and dangerous ketoacidosis, and when to get help.
This is general educational information, not medical advice. Moderate or large ketones with nausea or vomiting, abdominal pain, fast or deep breathing, fruity-smelling breath, confusion or severe drowsiness are an emergency: seek urgent medical help. If you have diabetes, follow your own care plan.
What ketones are and why they show up in urine
When your cells cannot get enough glucose, or when you eat little carbohydrate, the liver breaks down fat and produces ketones (ketone bodies, several of them acids) that tissues, including the brain, can use as fuel. Extra ketones are cleared by the kidneys and appear in the urine (the medical term is ketonuria).
Making ketones is a normal response to going without food. It becomes a problem when ketones build up faster than the body can handle, as happens in uncontrolled diabetes. That is why the same test result can be unremarkable in one person and urgent in another, and why context matters more than the number alone.
What trace, small, moderate and large ketones mean
Urine dipsticks report ketones in colour-coded grades. The mg/dL figures below are typical values for common strips; brands differ, so use the colour chart printed on your own strip or the range on your lab report.
| Dipstick result | Typical value (mg/dL) | Usual reading |
|---|---|---|
| Negative | 0 | No significant ketones |
| Trace | about 5 | Often harmless: fasting, low-carb eating, hard exercise or a skipped meal |
| Small | about 15 | Usually mild ketosis; check the context (diet, illness, blood sugar) |
| Moderate | about 40 | Significant ketone production; with diabetes or illness this needs prompt advice |
| Large | about 80 to 160 or more (the top of the scale varies by brand) | A lot of ketones; potentially dangerous, especially with diabetes, vomiting or feeling unwell |
In general, trace and small results are safe for most people with no symptoms, while moderate and large results are potentially dangerous and risk ketoacidosis. For anyone with diabetes, any positive result alongside a high blood sugar or illness deserves attention, and if you have diabetes or take an SGLT2 inhibitor, even trace or small results can matter when you are unwell.
Trace ketones in urine: should you worry?
A trace reading is the most searched result, and in most healthy people it is nothing to worry about. Common explanations are:
- an overnight fast or a long gap since your last meal
- a low-carbohydrate or ketogenic diet
- long or intense exercise
- a bout of vomiting or diarrhoea that left you eating little
- heavy alcohol use the day before
Because the strip reads the concentration of ketones, the same amount can look stronger in concentrated morning urine and fainter in dilute urine. See urine specific gravity for how concentration changes dipstick results.
The exceptions are people with diabetes (especially type 1) and people taking SGLT2-inhibitor diabetes medicines, for whom even a modest ketone reading with illness, vomiting or a rising blood sugar should trigger the steps in their care plan.
Common causes of ketones in urine
Normal or diet-related
- Fasting, including overnight, skipped meals and intermittent fasting
- Ketogenic or very low-carbohydrate diets
- Prolonged, intense exercise
Illness and circumstances
- Prolonged vomiting or diarrhoea, or an illness that stops you eating or drinking
- Alcohol, especially heavy drinking with little food (alcoholic ketoacidosis is a serious form, and in it a urine strip can look only mildly positive or even negative, because strips detect acetoacetate but not beta-hydroxybutyrate; symptoms matter more than the colour)
- Eating disorders and starvation
- Pregnancy, where vomiting or long gaps between meals can raise ketones, and where gestational diabetes also needs ruling out
Diabetes and medicines
- Diabetes with too little insulin, the main cause of dangerous ketone build-up (diabetic ketoacidosis, or DKA), most often in type 1 but possible in type 2
- SGLT2 inhibitors (a class of diabetes medicines), which can cause ketoacidosis even when the blood sugar is not very high
Ketosis vs ketoacidosis
Ketosis is the state of raised ketones. On a low-carbohydrate diet or during a fast, it is a normal metabolic state and usually causes few or only mild symptoms such as bad breath, headache or tiredness.
Ketoacidosis (DKA) is the dangerous situation in which ketones build up so much that the blood becomes acidic. Early signs include frequent urination, extreme thirst and dehydration, often with tiredness. Severe signs include nausea, vomiting, abdominal pain, fast or deep breathing, fruity-smelling breath, weakness and confusion. It usually comes with a high blood glucose in diabetes, but it can occur with near-normal glucose in people on SGLT2 inhibitors or after heavy alcohol use.
If you have diabetes, ask your care team for your own testing and action thresholds. Diabetes organisations commonly advise checking ketones when you are unwell, when blood glucose stays high, or during illness or stress. To see how high blood sugar appears on blood tests, see what your fasting glucose means and what your HbA1c means.
Urine ketone strips vs blood ketone tests
- Urine strips are cheap and easy, and mainly detect acetoacetate. They show what has recently been passed in urine, so they can lag behind what is happening in the blood right now, and they are affected by how dilute the urine is.
- Blood ketone meters measure beta-hydroxybutyrate and give a number. They are generally considered more accurate and more current, and they are preferred when a precise reading matters, such as in diabetes sick-day rules.
- Both need to be read with symptoms and blood glucose, not alone.
Ketones in urine during pregnancy
Ketones can appear in pregnancy when a person is vomiting, cannot eat or drink much, or goes long hours without food, and they can also occur with gestational diabetes. Do not try to manage them on your own. Tell your midwife or doctor about any ketones found on a urine test, and seek care promptly if you are vomiting repeatedly, cannot keep fluids down, or feel unwell.
How to use a urine ketone strip
- Check the expiry date and that the container has been kept closed, because strips that absorb moisture can give wrong colours.
- Collect fresh urine in a clean container, or briefly pass the strip through the stream, and do not touch the test pad.
- Tap off the excess and read the colour at exactly the time printed on your pack. Some brands specify as little as 15 seconds, and reading too early or too late shifts the grade.
- Compare with the chart on your own container in good light, and note the grade (negative, trace, small, moderate, large) rather than describing it from memory.
- Write down the context: when you last ate, any exercise, vomiting or alcohol, your blood sugar if you have diabetes. A ketone number without context is hard to interpret.
Why a reading can mislead
- Concentration: very dilute urine can hide a mild ketosis; very concentrated urine can exaggerate it.
- Timing: results can differ between first-morning and later urine, and after a fast.
- The strip itself: old, damaged or incorrectly stored strips, or reading the colour too early or late, can mislead.
- Medicines can cause false positives or odd colours, including levodopa (with dark urine), drugs containing sulfhydryl groups such as captopril or mesna, and urinary-pain dyes such as phenazopyridine. Tell the person reading your result what you take.
- A strip is not a diet scorecard: a stronger colour does not mean healthier, and a fainter colour on a keto diet does not mean the diet has stopped working.
What to do about ketones in urine
- Check the context. Did you fast, exercise hard, drink alcohol, vomit or change your diet?
- If you have diabetes, check your blood glucose, follow your sick-day plan and contact your care team as instructed.
- Drink fluids if you are able to and have no medical reason not to.
- Repeat the test later, ideally with a fresh strip, and note the colour grade rather than guessing.
- Look at the rest of the urinalysis, such as urine pH, nitrites, leukocyte esterase, occult blood and WBC in urine, and with blood tests such as CO₂ (bicarbonate) and the anion gap, which clinicians use when acid build-up is suspected.
- Do not skip your usual insulin or other prescribed medicine, and do not take extra doses, fast or restrict fluids, unless your care plan or care team tells you to.
When to talk to a doctor
- Moderate or large ketones, with or without diabetes, especially with illness, vomiting, a high blood sugar or any symptoms: seek urgent care.
- Ketones plus nausea or vomiting, abdominal pain, fast or deep breathing, fruity-smelling breath, confusion or severe drowsiness: this is an emergency, so call your local emergency number.
- Diabetes with ketones that stay high or a blood sugar that keeps rising, or you feel worse despite following your plan: call your care team or emergency services.
- Ketones while taking an SGLT2 inhibitor with nausea, vomiting, abdominal pain, tiredness or trouble breathing: get medical help immediately, even if your blood sugar is not very high.
- Ketones in pregnancy: mention them to your midwife or doctor at your next contact, and the same day if you are vomiting, cannot keep fluids down, have diabetes or feel unwell. In pregnancy with diabetes, ketones can develop at a lower blood sugar than usual, so follow your team's thresholds.
- Persistent trace or small ketones without an obvious reason such as fasting or diet: worth raising at your next appointment.
Related reading: urine specific gravity, urine pH, what your fasting glucose means, what your HbA1c means, the A1C to average glucose calculator, how to read your blood test results and tracking lab results over time.
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Frequently asked questions
What do ketones in urine mean?
Ketones (ketone bodies, several of them acids) are made by the body when it breaks down fat for energy instead of glucose. Small amounts in urine are common after fasting, a low-carbohydrate diet, prolonged exercise or illness with vomiting. Larger amounts, especially with a high blood sugar or symptoms such as vomiting, abdominal pain or fast breathing, can signal diabetic ketoacidosis, which is an emergency.
Are trace ketones in urine normal?
A trace result is common and usually harmless in someone without diabetes who has fasted, eaten little, exercised hard or is on a low-carbohydrate diet. Readings vary with how concentrated the urine is. If you have diabetes, a trace result is a reason to check your blood sugar and follow your care plan rather than ignore it.
What do moderate or large ketones in urine mean?
Moderate or large readings mean the body is producing a lot of ketones. In someone with diabetes, especially with a high blood sugar, this can indicate ketoacidosis and needs urgent medical advice. In someone without known diabetes it can follow prolonged vomiting, starvation or heavy alcohol use, but it can also signal undiagnosed diabetes or another serious condition, so it needs urgent medical advice the same day, and emergency care if you feel unwell.
Can you have ketones in urine without diabetes?
Yes. Fasting, a ketogenic or very low-carbohydrate diet, prolonged intense exercise, vomiting or diarrhoea, heavy alcohol use, eating disorders and pregnancy can all raise ketones without diabetes. Certain medicines, most often prescribed for diabetes (SGLT2 inhibitors), can also lead to ketoacidosis in people whose blood sugar is only mildly raised, so ketone symptoms on these medicines need urgent advice.
Are ketones in urine normal on a keto diet?
On a ketogenic diet it is expected that ketones rise and may appear in urine, often most clearly in the first weeks. Over time urine strips may show less. This is generally attributed to the body using ketones more efficiently, and strips detect only one type of ketone, so a fainter result does not by itself mean ketosis has stopped. A blood ketone meter is more reliable if you need to know. A positive strip on its own is not a measure of health or of weight loss.
Are ketones in urine during pregnancy dangerous?
They can be a sign that the body is short of carbohydrate, for example with morning sickness, vomiting or long gaps between meals, and in some cases of diabetes. Do not try to manage them on your own: tell your midwife or doctor about any ketones in urine, and seek care promptly if you are vomiting, cannot keep fluids down or feel unwell.
What is the difference between urine and blood ketone tests?
Urine strips mainly detect acetoacetate and show whether ketones are being passed out recently; they are cheap but can lag behind what is happening now and are affected by how dilute the urine is. Blood ketone meters measure beta-hydroxybutyrate directly and give a number, so they are considered more accurate and more current.
When should I go to the emergency room for ketones?
Seek urgent help if you have moderate or large ketones with nausea or vomiting, abdominal pain, fast or deep breathing, fruity-smelling breath, confusion or unusual drowsiness, or if you cannot keep fluids down. If you have diabetes and ketones stay high or you feel worse despite following your plan, call your care team or emergency services.
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