What Do Ketones in Your Urine Mean? Fasting, Keto, and When It's an Emergency
How to read a urine ketone result, from an overnight fast to a medical emergency.
Photo: Caroline Badran / Unsplash
Ketones in your urine usually mean your body is burning fat for fuel, for ordinary reasons such as an overnight fast, a ketogenic diet, a long workout, pregnancy, or a stomach bug that kept you from eating. Without diabetes, a trace or small result on a strip is usually not an emergency. With diabetes, the same result has to be read alongside blood sugar and how you feel. Ketones together with vomiting, belly pain, fast or deep breathing, or confusion are a reason to get urgent medical care.
Where do ketones come from?
Glucose is the body's first choice of fuel. When glucose is scarce, or there isn't enough insulin to move it into cells, the body breaks down stored fat and the liver turns the released fatty acids into ketone bodies, mainly beta-hydroxybutyrate and acetoacetate. In a review on measuring ketones published in 2023, Huang and colleagues described ketones as an energy source the liver makes during states of low carbohydrate availability, such as fasting or prolonged exercise.
Things are different when insulin is missing. The same review explained that during insulin deficiency, fat breakdown increases and the liver converts a flood of fatty acids into ketones. Ketones are acids, and when enough build up, the blood becomes acidic, which is diabetic ketoacidosis (DKA).
How does nutritional ketosis differ from DKA?
A urine ketone result makes more sense read next to blood sugar and whether there is any acidosis than read on its own. Here's how I read the ketone pad on a urinalysis:
- On an ordinary diet that includes carbohydrates, urine ketones should be negative.
- On a ketogenic diet, trace to small ketones can be expected, with normal glucose and no acidosis.
- In someone without diabetes, moderate ketones with normal or low glucose and no significant acidosis can be a sign of not eating enough, the effects of starvation.
- High ketones together with acidosis are an emergency. With high blood sugar or a history of diabetes, that is DKA.
The 2024 consensus report on hyperglycemic crises, from the American Diabetes Association and four other diabetes organizations (first author Guillermo Umpierrez), puts numbers on that last line. DKA requires all three of these: glucose of 200 mg/dL or higher (or a known history of diabetes, whatever the glucose), raised ketones, and metabolic acidosis. The authors recommend measuring blood beta-hydroxybutyrate, and they report that a level of 3.0 mmol/L or higher correlates well with the acid changes of DKA, with more than 90% sensitivity and specificity. In plain terms, more than nine in ten people with DKA would have a level at or above that cutoff, and more than nine in ten people checked for DKA who don't have it would have a level below it. The report also counts urine ketones of 2+ or more as significant ketosis, and uses a blood pH below 7.30 or a bicarbonate below 18 mmol/L as markers of acidosis.
In one small 2023 Oxford study, nutritional ketosis was well below that line. Ozoran and colleagues studied 15 adults with type 1 diabetes who had chosen their own diets. Average beta-hydroxybutyrate was 1.2 mmol/L in the six eating under 50 g of carbohydrate a day, and 0.3 and 0.1 in the groups eating more. The authors called this much lower than they expected and significantly lower than the level associated with DKA, though safety still needs evaluating in large randomized trials.
The consensus also lists other causes of raised ketones, including starvation (suggested by intake under about 500 calories a day), alcohol, and pregnancy.
Why can a urine strip be misleading?
Most urine strips use a reaction called nitroprusside, which detects acetoacetate but not beta-hydroxybutyrate, the main ketoacid in DKA. The consensus authors explain that urine can underestimate how severe ketosis is early on, because acetoacetate forms later, and overestimate it later, as beta-hydroxybutyrate is converted into acetoacetate. Huang's review made a similar point about the later stage: a urine test might still be rising even as DKA improves. The consensus report also names sulfhydryl medications such as captopril and valproate that can give false-positive urine results. For diagnosis and monitoring, the panel recommends measuring beta-hydroxybutyrate in blood, either in a lab or with a fingerstick meter.
Most continuous glucose monitors measure glucose but not ketones. In August 2026 the FDA authorized the first sensor that tracks both, for people with diabetes who use insulin or an SGLT2 inhibitor, with a US launch planned for later this year. Our post on CGMs for people without diabetes covers what a glucose reading can and can't tell you.
When are ketones an emergency?
The consensus report describes nausea, vomiting and abdominal pain in more than half of people with DKA, along with deep, rapid breathing that can carry a fruity smell from acetone. DKA can develop over hours to a few days.
DKA can also happen when blood sugar looks close to normal. The panel defines this euglycemic DKA as glucose below 200 mg/dL with the ketone and acidosis findings of DKA, and says SGLT2 inhibitors now account for the majority of these cases. SGLT2 inhibitors are a class of diabetes medicines whose generic names end in -gliflozin. In people with type 2 diabetes taking them, the panel lists very-low-carbohydrate diets, prolonged fasting, dehydration, excessive alcohol intake and the presence of autoimmunity as risk factors. In one series the report cites, 35% of people on an SGLT2 inhibitor who came in with DKA had glucose below 200 mg/dL. For someone on one of these medicines, a normal-looking glucose doesn't rule DKA out.
If you take an SGLT2 inhibitor and are considering a ketogenic diet or a long fast, bring it up with your prescriber before you start, and please don't change the medication on your own. The report notes that home blood ketone testing can help identify DKA early.
If your strip comes back positive
Without diabetes, a trace or small result while you are fasting, eating very low carb, or recovering from a hard workout can be ordinary nutritional ketosis. Feeling unwell, being unable to keep food down, or moderate or high ketones without an obvious cause are reasons to see a clinician. With diabetes, read the result with your blood glucose and, ideally, a blood ketone reading, under your care team's sick-day plan.
For another blood sugar result that needs context, see our post on a normal A1c with high fasting insulin, and the rest of this series is on the diabetes and metabolic health hub.
If you want a more structured approach to metabolic health, the Wayfinder's Well membership includes the full educational library, and Beyond Blood Sugar, an upcoming course on diabetes, will arrive in three parts.
FAQ
Is it normal to have ketones in your urine without diabetes?
It can be. Trace or small urine ketones can appear after an overnight fast, on a ketogenic diet, after long exercise, or when illness keeps you from eating. If you feel well and you don't have diabetes, a result like that usually reflects your body burning fat for fuel. If you feel unwell or can't keep food down, that's a reason to get checked.
What ketone level is dangerous?
In the 2024 consensus report on hyperglycemic crises, a blood beta-hydroxybutyrate of 3.0 mmol/L or higher correlated well with the acid changes of DKA, and the report treats urine ketones of 2+ or more as significant. DKA is diagnosed when raised ketones come together with acidosis and either high glucose or a history of diabetes. Separately from the report, anyone with diabetes who has moderate or high ketones should contact their care team the same day.
Can you have DKA with normal blood sugar?
Yes. This is called euglycemic DKA, which the 2024 consensus report defines as glucose below 200 mg/dL with the ketone and acidosis findings of DKA. The report says SGLT2 inhibitors, a class of diabetes medicines whose generic names end in -gliflozin, now account for the majority of these cases.
Is a blood ketone test more accurate than a urine strip?
For DKA, yes. Most urine strips detect acetoacetate but not beta-hydroxybutyrate, the main ketone in DKA, and urine results can lag behind what is happening in the blood. The 2024 consensus report recommends measuring blood beta-hydroxybutyrate, from a lab or a fingerstick meter, to diagnose and monitor DKA.
Can pregnancy cause ketones in urine?
Yes. The 2024 consensus report lists ketosis of pregnancy and hyperemesis, which is severe vomiting in pregnancy, among the causes of raised ketones that clinicians consider. If you are pregnant, your obstetric provider will want to hear about any positive ketone result.
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