High Blood Sugar and Diabetic Ketoacidosis (DKA)

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Last reviewed: October 9, 2026 · Sources: CDC, NIH/NIDDK, American Diabetes Association

Hyperglycemia means high blood glucose. Most people with diabetes experience it from time to time, and short periods are usually not dangerous. But ongoing high glucose damages the body over time, and very high glucose, especially with too little insulin, can lead to emergencies such as diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS). This guide explains causes, symptoms, what to do, and when to get emergency care.

What is hyperglycemia?

Hyperglycemia occurs when there is too much glucose in the blood because the body has too little insulin or cannot use insulin properly. What counts as "high" depends on your targets. For many nonpregnant adults with diabetes, the American Diabetes Association suggests keeping glucose below 180 mg/dL one to two hours after the start of a meal and between 80 and 130 mg/dL before meals. Your care team will tell you what level should prompt action and when to call them. MedlinePlus offers an overview of high blood sugar.

Common causes

Eating more carbohydrates than planned
Missing or not taking enough diabetes medicine or insulin
Less physical activity than usual
Illness or infection, which release stress hormones that raise glucose
Emotional stress
Some medicines, such as corticosteroids
Insulin that has gone bad due to heat or age, or a problem with an insulin pump or infusion site
The "dawn phenomenon," an early-morning rise in glucose caused by natural hormone changes

Symptoms of high blood sugar

Increased thirst and dry mouth
Frequent urination
Fatigue
Blurred vision
Headache
Difficulty concentrating

Over weeks and months, high blood sugar may cause unintended weight loss, slow-healing wounds, and frequent infections. Some people feel few symptoms at all, which is why monitoring matters. See checking blood sugar and CGMs.

What to do when your blood sugar is high

Follow your plan. Your care team may have given you instructions, such as a correction dose of insulin. Use only the doses your provider prescribed.
Drink water or other sugar-free fluids to stay hydrated.
Check for ketones if you have type 1 diabetes or have been told to, especially when glucose is high, for example above 240 mg/dL, or when you are sick. Ketones can be checked with urine strips or a blood ketone meter.
Look for a cause, such as a missed dose, a larger meal, illness, or a pump issue, so you can prevent it next time.
Be careful with exercise. Activity can lower glucose, but if you have type 1 diabetes with high glucose and ketones, avoid vigorous exercise because it can make things worse.
Recheck as your care team advises.

Contact your care team if your glucose stays above your target range for several readings, especially if you are sick or have ketones.

Diabetic ketoacidosis (DKA)

DKA is a serious, life-threatening complication. When there is not enough insulin, the body cannot use glucose for energy, so it breaks down fat at a rapid rate. This produces acids called ketones. As ketones build up, the blood becomes acidic. At the same time, high glucose pulls fluid out of the body through the urine, causing dehydration. According to MedlinePlus, DKA is most common in people with type 1 diabetes, and it is sometimes the first sign of type 1 diabetes in people who have not yet been diagnosed. It can also occur in people with type 2 diabetes.

What triggers DKA?

New, undiagnosed type 1 diabetes
Missed insulin doses or interrupted insulin delivery (for example, a blocked pump tube or dislodged infusion set)
Illness or infection
Heart attack, stroke, or other major medical stress
Certain medicines; for example, SGLT2 inhibitors have been linked to DKA, sometimes with blood glucose that is not very high
Alcohol or drug use

Symptoms of DKA

DKA usually develops over hours. The CDC lists nausea, vomiting, and stomach pain among signs that can occur with type 1 diabetes. Other symptoms may include:

Very high thirst and frequent urination
Fatigue and weakness
Deep, rapid breathing
Fruity-smelling breath
Flushed face, dry skin and mouth
Confusion or decreased alertness
High ketone levels in blood or urine

What to do

DKA is a medical emergency. Call 911 or go to the emergency department if you have high glucose with moderate or large ketones, vomiting and cannot keep fluids down, trouble breathing, confusion, or fruity breath. Do not try to manage suspected DKA at home without guidance. In the hospital, treatment typically includes intravenous fluids, insulin, and replacement of electrolytes such as potassium, along with treatment of the underlying cause.

Hyperosmolar hyperglycemic state (HHS)

HHS is another emergency, more common in people with type 2 diabetes, especially older adults. It involves extremely high blood glucose and severe dehydration, usually with few or no ketones. It often develops over days to weeks, frequently triggered by an infection or other illness and not drinking enough fluids. Symptoms can include extreme thirst, frequent urination that may later decrease, dry mouth, weakness, confusion, drowsiness, vision changes, and in severe cases seizures or coma. HHS requires emergency medical care.

Long-term effects of high blood sugar

Even without an emergency, glucose that stays high over months and years can damage blood vessels and nerves. NIDDK describes how diabetes can lead to heart disease, stroke, kidney disease, eye disease, nerve damage, and foot problems. Keeping A1C near your goal lowers these risks. See A1C and blood sugar targets.

Preventing hyperglycemia and DKA

Take insulin and other medicines as prescribed, and never stop insulin entirely if you have type 1 diabetes, even when you are not eating.
Follow a meal plan and stay active. See eating basics and exercise.
Store insulin properly and do not use expired insulin.
If you use a pump, know how to check for and fix delivery problems, and keep backup supplies such as pens or syringes.
Have a written sick-day plan, including when to check ketones and when to call. See managing diabetes when sick.
Keep ketone strips that are not expired if your care team recommends them.
Review high patterns with your care team so your treatment can be adjusted.

Key takeaways

Hyperglycemia is high blood glucose; occasional highs are common, but persistent highs cause long-term damage.
Stay hydrated, follow your plan, check ketones when advised, and contact your care team for persistent highs.
DKA (high ketones, more common in type 1) and HHS (extreme glucose and dehydration, more common in type 2) are emergencies.
Vomiting, rapid breathing, fruity breath, or confusion with high glucose need immediate medical care.

Sources

Links to the sources cited above appear in the text. We rely on the Centers for Disease Control and Prevention (CDC), the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), and the American Diabetes Association (ADA).

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