Hyperglycemia (High Blood Sugar)

Hyperglycemia (high blood sugar) is common in people who have diabetes. If it’s left untreated, chronic hyperglycemia can lead to diabetes complications, such as nerve damage, eye disease and kidney damage.


What is hyperglycemia (high blood sugar)?

Hyperglycemia happens when there’s too much sugar (glucose) in your blood. It’s also called high blood sugar or high blood glucose. This happens when your body has too little insulin (a hormone) or if your body can’t use insulin properly (insulin resistance).

Hyperglycemia usually means you have diabetes, and people with diabetes can experience hyperglycemia episodes frequently.

If you have hyperglycemia that’s untreated for long periods of time, it can damage your nerves, blood vessels, tissues and organs.

Severe hyperglycemia can also lead to an acute (sudden and severe) life-threatening complication called diabetes-related ketoacidosis (DKA), especially in people with diabetes who take insulin or people with undiagnosed Type 1 diabetes. This requires immediate medical treatment.

What blood sugar level is hyperglycemia?

For people undiagnosed with diabetes, hyperglycemia is blood glucose greater than 125 mg/dL (milligrams per deciliter) while fasting (not eating for at least eight hours).

A person has prediabetes if their fasting blood glucose is 100 mg/dL to 125 mg/dL.

A person with a fasting blood glucose greater than 125 mg/dL on more than one occasion usually receives a diabetes diagnosis — typically Type 2 diabetes. People with Type 1 diabetes usually have very high blood sugar (above 250 mg/dL) upon diagnosis.

For a person with diabetes, hyperglycemia is usually considered to be a blood glucose level greater than 180 mg/dL one to two hours after eating. But this can vary depending on what your target blood sugar goals are.

What is blood sugar?

Glucose (sugar) mainly comes from carbohydrates in the food and drinks you consume. It’s your body’s main source of energy. Your blood carries glucose to all of your body’s cells to use for energy.

If you don’t have diabetes, several bodily processes naturally help keep your blood glucose in a healthy range. Insulin, a hormone your pancreas makes, is the most significant contributor to maintaining healthy blood sugar.

High blood sugar most often happens due to a lack of insulin or insulin resistance. This leads to diabetes. People who have diabetes must use medication, like oral diabetes medications or synthetic insulin, and/or lifestyle changes to help keep their blood sugar levels in range.


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How common is hyperglycemia?

Hyperglycemia and diabetes are very common — about 1 in 10 people in the United States has diabetes. Hyperglycemia episodes are also very common in people with diabetes.

Symptoms and Causes

Symptoms of hyperglycemia include increased thirst, frequent urination, headache, blurred vision, fatigue and more.
If you have these symptoms, you should see a healthcare provider. If you have these symptoms in addition to vomiting and/or labored breathing, seek immediate medical help.

What are the signs and symptoms of hyperglycemia?

Early symptoms of hyperglycemia include:

Symptoms of long-term hyperglycemia include:

You should see your healthcare provider if you or your child is experiencing these symptoms.

The glucose level at which people with diabetes start to experience symptoms varies. Many people don’t experience symptoms until their blood sugar is 250 mg/dL or higher. People who haven’t yet been diagnosed with diabetes typically experience these symptoms at lower levels.

It’s especially important to know the early signs of hyperglycemia and to monitor your blood sugar regularly if you take insulin or other medications for diabetes. If hyperglycemia is left untreated, it can develop into diabetes-related ketoacidosis (DKA), in which a lack of insulin and a high amount of ketones cause your blood to become acidic. DKA can also affect people who have undiagnosed Type 1 diabetes. This condition is an emergency situation that can lead to coma or death.

Symptoms of ketoacidosis include:

Seek immediate medical help if you or your child is experiencing symptoms of DKA.


What causes hyperglycemia?

Hyperglycemia most often results from a lack of insulin. This can happen due to insulin resistance and/or issues with your pancreas — the organ that makes insulin.

Other hormones can contribute to the development of hyperglycemia as well. Excess cortisol (the “stress hormone”) or growth hormone, for example, can lead to high blood sugar:

Insulin resistance

A common cause of hyperglycemia is insulin resistance. Insulin resistance, also known as impaired insulin sensitivity, happens when cells in your muscles, fat and liver don’t respond as they should to insulin.

When your cells don’t properly respond to insulin, your body requires more and more insulin to regulate your blood sugar. If your body is unable to produce enough insulin (or you don’t inject enough insulin), it results in hyperglycemia.

Insulin resistance is the main cause of Type 2 diabetes, but anyone can experience it, including people without diabetes and people with other types of diabetes. It can be temporary or chronic.

Common causes of insulin resistance include:

  • Obesity. Scientists believe obesity, especially excess fat tissue in your belly and around your organs (visceral fat), is a primary cause of insulin resistance.
  • Physical inactivity.
  • A diet of highly processed, high-carbohydrate foods and saturated fats.
  • Certain medications, including corticosteroids, some blood pressure medications, certain HIV treatments and some psychiatric medications. These may cause temporary or long-term insulin resistance depending on how long you take them.

Certain hormonal conditions can lead to insulin resistance, such as:

Certain inherited genetic conditions are also associated with insulin resistance, including:

  • Rabson-Mendenhall syndrome.
  • Donohue syndrome.
  • Myotonic dystrophy.
  • Alström syndrome.
  • Werner syndrome.

Pancreas issues

Damage to your pancreas can lead to a lack of insulin production and hyperglycemia. Pancreatic conditions that can cause hyperglycemia and diabetes include:

  • Autoimmune disease: In Type 1 diabetes, your immune system attacks the insulin-producing cells in your pancreas for unknown reasons. This means your pancreas can no longer make insulin, resulting in hyperglycemia. Latent autoimmune diabetes in adults (LADA) also results from an autoimmune reaction, but it develops much more slowly than Type 1.
  • Chronic pancreatitis: This condition causes prolonged inflammation of your pancreas, which can damage the cells that produce insulin. This can result in a lack of insulin and hyperglycemia. Pancreatitis is a known cause of Type 3c diabetes.
  • Pancreatic cancer: Cancer in your pancreas can damage the cells that produce insulin, resulting in a lack of insulin and hyperglycemia. About 25% of people with pancreatic cancer are diagnosed with diabetes 6 months to 36 months before the diagnosis of pancreatic cancer.
  • Cystic fibrosis: People who have cystic fibrosis develop excessive mucus, which can scar their pancreas. This can cause their pancreas to produce less insulin, resulting in hyperglycemia and cystic fibrosis-related diabetes (CFRD).

Temporary causes of hyperglycemia

Certain situations can temporarily increase your blood sugar levels and cause hyperglycemia in people with and without diabetes.

Physical stress, such as from an illness, surgery or injury, can temporarily raise your blood sugar. Acute emotional stress, such as experiencing trauma or work-related stress, can increase your blood sugar as well. This is because your body releases cortisol and/or epinephrine (adrenaline).

Causes of hyperglycemia in people with diabetes

Several factors can contribute to hyperglycemia in people with diabetes. It can develop if things like food and diabetes medications are out of balance.

Common situations that can lead to hyperglycemia for people with diabetes include:

  • Not taking enough insulin, injecting the wrong insulin or expired insulin, or an issue with the injection (such as from a site issue in insulin pump therapy).
  • Not timing insulin and carb intake correctly.
  • The amount of carbohydrates you’re consuming isn’t balanced with the amount of insulin your body can make or the amount of insulin you inject.
  • The dose of oral diabetes medication you’re taking is too low for your needs.
  • Being less active than usual.
  • Dawn phenomenon.

What are the complications of hyperglycemia?

Prolonged (chronic) hyperglycemia over the years can damage blood vessels and tissues in your body. This can lead to a variety of complications, including the following:

It’s important to remember that other factors can contribute to the development of diabetes complications, such as genetics and how long you’ve had diabetes.

Acute (sudden and severe) hyperglycemia can lead to DKA, which is life-threatening.


Diagnosis and Tests

How is hyperglycemia diagnosed?

Healthcare providers order bloodwork to screen for hyperglycemia and diagnose diabetes. These tests may include:

People with diabetes use at-home blood sugar testing (using a glucose meter) to monitor their blood sugar and check for hyperglycemia. If you use continuous glucose monitoring (CGM), your device may alert you to high blood sugar. As this technology can sometimes be inaccurate, it’s important to check your blood sugar with a glucose meter if the CGM reading doesn’t match how you feel.

Management and Treatment

How is hyperglycemia treated?

If you take insulin to manage diabetes, injected insulin is the main way to treat hyperglycemia episodes. Everyone requires different insulin doses. You and your healthcare provider will determine which dose is best for you to treat and prevent high blood sugar. Dietary changes and exercise plans can also help manage your blood sugar to prevent hyperglycemia.

For people with Type 2 diabetes who don’t require injected insulin, lifestyle changes, such as dietary changes and exercise, as well as oral diabetes medications, can help manage hyperglycemia. You and your provider will determine the plan that’s best for you.


How can I prevent hyperglycemia episodes?

Unfortunately, it can be difficult to totally prevent high blood sugar when you have diabetes. But you can adjust your diabetes management plan to try to reduce the number of hyperglycemia episodes you experience.

It’s easiest to do this when you and your healthcare provider understand what causes your blood sugar to rise. Give your healthcare provider as much information as possible about any high blood sugar episodes. Fixing the problem may be as simple as changing the times you take medication, eat and exercise.

The following steps can help prevent high blood sugar:

  • Take all your medications as prescribed.
  • Follow your healthcare provider’s instructions about food and exercise.
  • Check your blood sugar regularly.

Outlook / Prognosis

What can I expect if I have hyperglycemia?

The prognosis (outlook) of people with hyperglycemia varies based on how well they manage their diabetes overall.

Several factors affect how well a person can manage diabetes, including:

  • Access to healthcare services.
  • Access to diabetes education.
  • Access to diabetes management technology and medication.
  • Access to healthy dietary and exercise resources.
  • Support from loved ones.
  • Mental health conditions, such as depression and anxiety.
  • Other physical health conditions.

Chronic hyperglycemia can cause severe complications, and the complications are usually irreversible. Several studies have shown that untreated chronic hyperglycemia shortens lifespans and worsens the quality of life.

It’s important to know that you can live a healthy life with diabetes. The following are key to a better prognosis:

  • Lifestyle changes.
  • Regular exercise.
  • Dietary changes.
  • Regular blood sugar monitoring, especially for those who take insulin.

Studies have shown that people with diabetes may be able to reduce the risk of complications by consistently keeping their A1C levels below 7%.

Living With

When should I see my healthcare provider about hyperglycemia?

If you have diabetes and are experiencing frequent high blood sugar episodes, talk to your provider who helps you manage diabetes. They can help you adjust your management plan, which may include changes to your medication regimen, meal plans or exercise routine.

When should I go to the ER?

If you’re experiencing symptoms of DKA, such as high blood sugar with vomiting and extreme thirst, go to the emergency room. DKA requires immediate medical treatment.

Additional Common Questions

What’s the difference between hyperglycemia and hypoglycemia?

Hyperglycemia is high blood sugar. “Hyper-” means “above” or “beyond.” Hypoglycemia is low blood sugar. “Hypo-” means “below.”

A note from Cleveland Clinic

Hyperglycemia is quite common in people with diabetes. Monitoring your blood sugar regularly and seeing your diabetes healthcare provider regularly can help you properly manage diabetes and hyperglycemia. It’s important to remember that high blood sugar doesn’t have to be chronic. Know that there are steps you can take to prevent it. If you’re feeling overwhelmed with diabetes management, talk to your healthcare provider. Together, you can formulate a plan to get closer to your management goals.

Medically Reviewed

Last reviewed on 03/02/2023.

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