Ketones in urine mean your body is burning fat for fuel instead of its preferred energy source, glucose. In small amounts, this can be completely normal, especially if you’ve been fasting, exercising hard, or eating very few carbohydrates. In larger amounts, particularly if you have diabetes, ketones in urine can signal a dangerous condition called diabetic ketoacidosis (DKA) that needs immediate medical attention.
How Your Body Makes Ketones
Your cells normally run on glucose, the sugar that comes from carbohydrates in food. When glucose is scarce, your liver switches to a backup system: it breaks down stored fat into molecules called ketone bodies. This process happens inside the liver’s mitochondria, where fatty acids are converted step by step into three types of ketones that dissolve easily in your blood and travel to your brain, heart, and muscles as alternative fuel.
Your kidneys filter excess ketones out of your blood and into your urine. That’s why a urine test can pick them up. A small amount means your body is tapping into fat stores. A large amount means ketone production has outpaced your body’s ability to use them, and they’re accumulating.
Common Causes Without Diabetes
Plenty of everyday situations trigger mild ketone production in people who don’t have diabetes:
- Skipping meals or fasting. Going without food for an extended period depletes your glucose supply and shifts your body toward fat burning.
- Low-carb or keto diets. Deliberately cutting carbohydrates puts your body into a state called nutritional ketosis, where low-level ketone production is the intended effect.
- Intense exercise. A hard workout can burn through your available glucose, especially if you haven’t eaten enough beforehand.
- Dehydration. When you’re dehydrated, ketones become more concentrated in your urine, making them more likely to show up on a test even if production is modest.
- Illness with vomiting or diarrhea. Being sick can make it hard to eat or keep food down, which depletes glucose and triggers fat breakdown.
In these situations, ketones typically resolve once you eat, drink fluids, or recover from the illness. They’re a sign your metabolism is adapting, not a sign something is wrong.
When Ketones Signal a Problem
For people with diabetes, especially type 1, ketones in urine carry a very different meaning. When your body can’t produce enough insulin (or you’ve missed doses), glucose builds up in your blood but can’t actually get into your cells. Your cells are starving despite high blood sugar, so your liver ramps up ketone production dramatically. This leads to diabetic ketoacidosis, where ketones accumulate so fast they make your blood acidic.
DKA is diagnosed when three things are present at the same time: blood sugar at or above 200 mg/dL, a blood ketone level at or above 3 mmol/L (or a urine ketone strip reading of 2+ or higher), and acidic blood chemistry. It develops over hours to days, not instantly, which means there’s a window to catch it early.
The early warning signs are feeling extremely thirsty and urinating far more than usual. If it progresses, symptoms escalate quickly: nausea and vomiting, stomach pain, fruity-smelling breath, fast deep breathing, dry skin and mouth, headache, muscle aches, and severe fatigue. Fruity breath is one of the most distinctive signs because it comes from acetone, one of the three ketone types, being exhaled through your lungs.
How Urine Ketone Tests Work
Most urine ketone tests use a simple dip strip. You urinate into a container, dip the test strip in, and wait for it to change color. You then compare the strip’s color to a chart that comes with the kit, which shows a range from negative (no ketones) through trace, small, moderate, and large amounts.
One important limitation: urine strips don’t reflect your ketone levels right now. They show what your levels were over the past few hours, since it takes time for ketones to filter from your blood into your urine. Blood ketone meters are more precise and give a real-time reading. For blood tests, a level below 0.6 mmol/L is normal. Between 0.6 and 1.5 mmol/L indicates low to moderate risk. Above 1.6 mmol/L is considered high risk for DKA, and above 3.0 mmol/L is very high risk.
If you’re on a keto diet and testing your urine out of curiosity, trace to small amounts of ketones are expected and reflect that your body is in nutritional ketosis. Moderate or large readings are not typical for nutritional ketosis and deserve attention.
Ketones During Pregnancy
Pregnant women sometimes show ketones in urine during routine prenatal checkups. The most common reasons mirror the non-diabetic causes: dehydration, skipping meals, or severe morning sickness that makes it impossible to keep food down. Pregnancy increases your body’s energy demands, so even short gaps without eating can push your metabolism toward fat burning faster than usual.
Persistent or high ketone levels during pregnancy matter because they can indicate that you’re not getting enough nutrition, whether from prolonged vomiting, inadequate calorie intake, or an underlying illness. If morning sickness is severe enough to cause repeated ketone-positive urine tests, your provider will likely want to address the vomiting directly and ensure you’re staying hydrated and nourished.
What To Do About Ketones in Urine
Your response depends entirely on context. If you don’t have diabetes and you tested positive after fasting, skipping a meal, or working out hard, eating a balanced meal and drinking water is usually all it takes. Retest in a few hours, and the ketones will likely be gone.
If you have diabetes, the American Diabetes Association recommends contacting your care team immediately when urine tests show moderate or large ketones. If you can’t reach them, go to an emergency room or urgent care facility. One critical rule: never exercise when ketones are moderate or large and your blood sugar is high. Exercise can actually worsen ketone production in that situation because it increases your body’s energy demand without resolving the underlying insulin problem.
Seek emergency care if your blood sugar stays at or above 300 mg/dL, your breath smells fruity, you’re vomiting and unable to keep fluids down, or you’re having difficulty breathing. DKA is treatable, but it requires medical intervention to correct the insulin deficit and restore your body’s acid balance.