Ketones in Urine: What They Mean and When to Test

What ketones are

When cells cannot get enough glucose, usually because there is not enough insulin or because food is limited, the body burns fat instead. That produces ketones, which can build up in blood and urine. MedlinePlus says that having some ketones in the urine is normal. In diabetes the concern is a shortage of insulin: ketones rise, the blood becomes acidic, and that is diabetic ketoacidosis. The CDC says the two most common causes are illness and missed or incorrect insulin, such as missed shots, a clogged pump or the wrong dose. It lists heart attack, stroke, injury, alcohol or drug use and some medicines as other causes.

When to test

• When sick, or when blood sugar is 250 mg/dL or higher (CDC). Check blood sugar every 4 to 6 hours and test for ketones.
• When glucose is high or you feel unwell (ADA). The ADA prefers a blood ketone meter to urine strips and says to keep supplies on hand and check expiry dates.
• Other times a charity suggests: Breakthrough T1D lists glucose above 240 mg/dL for 3 hours with a pump or automated insulin delivery, and above 300 mg/dL for 3 hours on injections, and before exercise if glucose is above 240 mg/dL. These are not ADA numbers; ask your care team for yours.

This page does not tell you what to do about insulin. Follow your own sick-day plan, and call your care team if you do not have one.

How to read a urine strip

Strips change color in a few seconds after contact with urine, and you compare to the chart on the bottle. Follow the package directions exactly, including the time to read. Results are reported as negative, trace, small, moderate or large. Brands print the strengths differently, so use your own chart.

Source: Breakthrough T1D. The ADA page we reviewed gives a blood threshold but no urine categories. The ketone levels chart has the blood bands.

Ketones without diabetes

MedlinePlus lists several reasons for ketones in people without diabetes: long vomiting or diarrhea, a low-carbohydrate keto diet, fasting or starvation, very long or hard exercise, alcohol use disorder, eating disorders and pregnancy. Severe symptoms such as vomiting, belly pain, confusion, trouble breathing or fruity breath need immediate medical help in anyone.

What to do next

1. Recheck blood sugar and ketones as your plan says.
2. Drink fluids unless your care team told you otherwise.
3. Call your care team for any positive result when sick.
4. Write the readings down in the blood sugar log to bring with you.

Information only, not medical advice. Your care team may set different targets for you, and only a lab test ordered by a clinician can diagnose diabetes or prediabetes. See our medical disclaimer.