High blood sugar, also called hyperglycemia, affects people who have diabetes. Several factors can play a role in hyperglycemia in people with diabetes. They include food and physical activity, illness, and medications not related to diabetes. Skipping doses or not taking enough insulin or other medication to lower blood sugar also can lead to hyperglycemia.

It's important to treat hyperglycemia. If it's not treated, hyperglycemia can become severe and cause serious health problems that require emergency care, including a diabetic coma. Hyperglycemia that lasts, even if it's not severe, can lead to health problems that affect the eyes, kidneys, nerves and heart.


Hyperglycemia usually doesn't cause symptoms until blood sugar (glucose) levels are high — above 180 to 200 milligrams per deciliter (mg/dL), or 10 to 11.1 millimoles per liter (mmol/L).

Symptoms of hyperglycemia develop slowly over several days or weeks. The longer blood sugar levels stay high, the more serious symptoms may become. But some people who've had type 2 diabetes for a long time may not show any symptoms despite high blood sugar levels.

Early signs and symptoms

Recognizing early symptoms of hyperglycemia can help identify and treat it right away. Watch for:

  • Frequent urination
  • Increased thirst
  • Blurred vision
  • Feeling weak or unusually tired

Later signs and symptoms

If hyperglycemia isn't treated, it can cause toxic acids, called ketones, to build up in the blood and urine. This condition is called ketoacidosis. Symptoms include:

  • Fruity-smelling breath
  • Dry mouth
  • Abdominal pain
  • Nausea and vomiting
  • Shortness of breath
  • Confusion
  • Loss of consciousness

When to see a doctor

Seek immediate help from your care provider or call 911 if:

  • You have ongoing diarrhea or vomiting, and you can't keep any food or fluids down
  • Your blood glucose levels stay above 240 milligrams per deciliter (mg/dL) (13.3 millimoles per liter (mmol/L)) and you have symptoms of ketones in your urine


During digestion, the body breaks down carbohydrates from foods — such as bread, rice and pasta — into sugar molecules. One of the sugar molecules is called glucose. It's one of the body's main energy sources. Glucose is absorbed and goes directly into your bloodstream after you eat, but it can't enter the cells of most of the body's tissues without the help of insulin. Insulin is a hormone made by the pancreas.

When the glucose level in the blood rises, the pancreas releases insulin. The insulin unlocks the cells so that glucose can enter. This provides the fuel the cells need to work properly. Extra glucose is stored in the liver and muscles.

This process lowers the amount of glucose in the bloodstream and prevents it from reaching dangerously high levels. As the blood sugar level returns to normal, so does the amount of insulin the pancreas makes.

Diabetes drastically reduces insulin's effects on the body. This may be because your pancreas is unable to produce insulin, as in type 1 diabetes. Or it may be because your body is resistant to the effects of insulin, or it doesn't make enough insulin to keep a normal glucose level, as in type 2 diabetes.

In people who have diabetes, glucose tends to build up in the bloodstream. This condition is called hyperglycemia. It may reach dangerously high levels if it is not treated properly. Insulin and other drugs are used to lower blood sugar levels.

Risk factors

Many factors can contribute to hyperglycemia, including:

  • Not using enough insulin or other diabetes medication
  • Not injecting insulin properly or using expired insulin
  • Not following your diabetes eating plan
  • Being inactive
  • Having an illness or infection
  • Using certain medications, such as steroids or immunosuppressants
  • Being injured or having surgery
  • Experiencing emotional stress, such as family problems or workplace issues

Illness or stress can trigger hyperglycemia. That's because hormones your body makes to fight illness or stress can also cause blood sugar to rise. You may need to take extra diabetes medication to keep blood glucose in your target range during illness or stress.


Long-term complications

Keeping blood sugar in a healthy range can help prevent many diabetes-related complications. Long-term complications of hyperglycemia that isn't treated include:

  • Cardiovascular disease
  • Nerve damage (neuropathy)
  • Kidney damage (diabetic nephropathy) or kidney failure
  • Damage to the blood vessels of the retina (diabetic retinopathy) that could lead to blindness
  • Feet problems caused by damaged nerves or poor blood flow that can lead to serious skin infections, ulcerations and, in some severe cases, amputation
  • Bone and joint problems
  • Teeth and gum infections

Emergency complications

If blood sugar rises very high or if high blood sugar levels are not treated, it can lead to two serious conditions.

  • Diabetic ketoacidosis. This condition develops when you don't have enough insulin in your body. When this happens, glucose can't enter your cells for energy. Your blood sugar level rises, and your body begins to break down fat for energy.

    When fat is broken down for energy in the body, it produces toxic acids called ketones. Ketones accumulate in the blood and eventually spill into the urine. If it isn't treated, diabetic ketoacidosis can lead to a diabetic coma that can be life-threatening.

  • Hyperosmolar hyperglycemic state. This condition occurs when the body makes insulin, but the insulin doesn't work properly. Blood glucose levels may become very high — greater than 600 mg/dL (33.3 mmol/L) without ketoacidosis. If you develop this condition, your body can't use either glucose or fat for energy.

    Glucose then goes into the urine, causing increased urination. If it isn't treated, diabetic hyperosmolar hyperglycemic state can lead to life-threatening dehydration and coma. It's very important to get medical care for it right away.


To help keep your blood sugar within a healthy range:

  • Follow your diabetes meal plan. If you take insulin or oral diabetes medication, be consistent about the amount and timing of your meals and snacks. The food you eat must be in balance with the insulin working in your body.
  • Monitor your blood sugar. Depending on your treatment plan, you may check and record your blood sugar level several times a week or several times a day. Careful monitoring is the only way to make sure that your blood sugar level stays within your target range. Note when your glucose readings are above or below your target range.
  • Carefully follow your health care provider's directions for how to take your medication.
  • Adjust your medication if you change your physical activity. The adjustment depends on blood sugar test results and on the type and length of the activity. If you have questions about this, talk to your health care provider.

Aug 20, 2022

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