Blood Sugar of 250 mg/dL: What It Means
250 mg/dL (13.9 mmol/L) is a high reading, and the line at which the CDC says to check for ketones. The CDC advice: if you have diabetes and are sick, or your blood sugar is 250 or higher, check your blood sugar every 4 to 6 hours and test for ketones.
Why 250 is a marker
High glucose by itself usually causes thirst and frequent urination. What worries clinicians at 250 and above is the risk of ketones, which build when the body lacks enough insulin to use glucose and starts burning fat. Ketones can lead to diabetic ketoacidosis (DKA), a medical emergency. That risk is highest in type 1 diabetes and when sick or when insulin is missed, though it can occur in other situations too. That is why the CDC puts 250 on its list of times to test.
What the CDC and ADA suggest you do
- Test for ketones. Urine strips or a blood ketone meter. The ketones in urine page explains the results and the ketone levels chart lists the bands.
- Check your blood sugar again every 4 to 6 hours while it stays high or you are ill (CDC).
- Follow your sick-day plan, and call your care team if you do not have one or ketones are present. We do not give insulin or medicine instructions.
- Drink water unless your care team told you otherwise, and know the emergency signs above.
If you wear a CGM
For most nonpregnant adults the ADA goal is under 5% of the time above 250 mg/dL, and under 25% above 180. Short spikes after meals are not the same as hours at 250 or more. The GMI calculator can show the share of your readings above 250. Persistent readings in that range are worth bringing to your care team.
Related reading
Compare with 200 after eating and 300. The chart shows all the lines side by side.
Frequently asked questions
Is a blood sugar of 250 an emergency?
Not by itself. But the CDC says to check your ketones when you are sick or your blood sugar is 250 mg/dL (13.9 mmol/L) or higher, and to get emergency help if it stays at 300 or you have DKA symptoms. Follow any sick-day plan from your care team.
What is 250 mg/dL in mmol/L?
13.9 mmol/L (250 ÷ 18).
How often should I check at 250?
The CDC says that if you have diabetes and are sick, or your blood sugar is 250 mg/dL or higher, check your blood sugar every 4 to 6 hours and test your urine for ketones. Your own plan may differ.
What is the time-in-range goal for readings above 250?
For CGM users, the ADA and the international consensus give a goal of under 5% of time above 250 mg/dL for most adults, and under 10% for older adults with complex health.
What are the signs I need urgent care?
Blood sugar that stays at 300 or above, fruity breath, vomiting with no fluids staying down, trouble breathing, or several DKA signs together. See the emergency box on this page.
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.
Sources
- CDC: Diabetic Ketoacidosis
- ADA: DKA (Ketoacidosis) & Ketones
- ADA Standards of Care in Diabetes—2026, Section 6: Glycemic Goals, Hypoglycemia, and Hyperglycemic Crises
- Battelino T et al. Clinical targets for CGM data interpretation: international consensus on time in range. Diabetes Care 2019;42:1593
Last reviewed: by the Diabetes Blogs editorial team. Information only, not medical advice.
