Hyperglycemia: What Is It?

Medically Reviewed by Jabeen Begum, MD on November 08, 2023
8 min read

Hyperglycemia (also called high blood sugar or high blood glucose) is when there's too much glucose (sugar) in your bloodstream, typically because your body isn't making or using insulin as well as it should. Insulin is a hormone that helps balance out your blood sugar levels.

Around 1 in 10 people in the United States have diabetes. Blood sugar control is at the center of any diabetes treatment plan. Hyperglycemia is a major concern, and can affect people with both type 1 and type 2 diabetes. There are two main kinds:

  • Fasting hyperglycemia. This is blood sugar for people who have diabetes that's higher than 130 mg/dL (milligrams per deciliter) after not eating or drinking for at least 8 hours. If your fasting blood glucose is 100 mg/dL to 125 mg/dL, this means you have prediabetes.
  • Postprandial or after-meal hyperglycemia. This is blood sugar that's higher than 180 mg/dL 2 hours after you eat. People without diabetes rarely have blood sugar levels over 140 mg/dL after a meal, unless it’s really large.

When it happens often or all the time, high glucose levels can cause damage to your nerves, blood vessels, and organs. It can also lead to other serious conditions. 

It's important to treat high blood sugar right away to help avoid more health problems.

Hyperglycemia vs. Hypoglycemia

These conditions are related to blood sugar, but they're very different. Hyperglycemia is when your blood sugar spikes too high, while hypoglycemia means your blood sugar level is lower than normal. 

As your body breaks down the food you eat, it turns carbs into a type of sugar called glucose, which gives you energy. Glucose goes into your bloodstream after you eat, but it needs insulin, a hormone from the pancreas, to get into your body's cells so they can use it. When your blood sugar rises, your pancreas releases insulin, letting glucose into cells. Your liver and muscles store extra glucose, which keeps your blood sugar levels normal. Diabetes interrupts this process. In type 2 diabetes, your body resists insulin or doesn't make enough of it, so sugar stays in your blood.

When you have diabetes, your blood sugar may rise if you:

  • Skip or forget your insulin or oral glucose-lowering medicine
  • Eat too many grams of carbohydrates for the amount of insulin you took, or eat too many carbs in general
  • Have an infection
  • Are sick
  • Are under stress
  • Become inactive or exercise less than usual
  • Take part in strenuous physical activity, especially when your blood sugar levels are high and insulin levels are low

Insulin resistance

A major reason why you may have hyperglycemia is insulin resistance. It's also the leading cause of type 2 diabetes. Insulin resistance happens when your muscle, fat, and liver cells react abnormally to insulin. As a result, your body needs higher amounts of insulin to balance out your blood sugar levels. If your body doesn't get the insulin it needs, you'll end up with hyperglycemia. 

Here are some reasons why you could have insulin resistance:

  • Obesity (especially extra weight around your belly and organs)
  • Lack of exercise
  • Eating high-processed, high-carbohydrate foods and saturated fats
  • Medicines such as corticosteroids and some blood pressure, HIV, and mental health treatments

The dawn phenomenon

Another possible reason for a spike in your blood sugar is what's called the dawn phenomenon. This is when your blood sugar rises in the morning, usually between 4 and 8 a.m. Researchers aren't sure what causes the dawn phenomenon. But they think when your body releases certain hormones (growth hormone, cortisol, and others) overnight, it boosts insulin resistance and raises your blood sugar.

Causes of high blood sugar in the morning include:

  • A lack of insulin the previous night
  • An incorrect dose of diabetes medicine the night before
  • Eating carbs before bedtime

Hyperglycemia in people without diabetes

People without diabetes can also have high blood sugar. Causes include:

  • Cushing's syndrome. This rare condition happens when your cortisol hormone levels stay raised for too long. One symptom of the disease is high blood sugar. 
  • Diseases of the pancreas. One job of your pancreas is to make insulin and glucagon and transport these hormones into your bloodstream. When a disease like pancreatitis or pancreatic cancer disrupts this process, it can cause high blood sugar.
  • Polycystic ovary syndrome (PCOS). This condition results from your ovaries making too much of sex hormones called androgens. Experts aren't sure what causes PCOS, but they do know many people with the condition have insulin resistance. 

Early hyperglycemia symptoms include:

  • Thirst
  • Headaches
  • Trouble concentrating
  • Blurred vision
  • Frequent peeing
  • Fatigue (weak, tired feeling)
  • Weight loss
  • Blood sugar more than 180 mg/dL

Ongoing high blood sugar may cause:

Diabetes-related ketoacidosis (DKA)

If hyperglycemia symptoms become too serious, you could form another life-threatening health problem called diabetes-related ketoacidosis (DKA). When you can't process glucose, your liver makes chemicals called ketones for your body to use for fuel. A lack of insulin coupled with too many ketones causes your blood to turn acidic. 

DKA tends to happen in people with diabetes who take insulin or those with type 1 diabetes but haven't been diagnosed. Symptoms of ketoacidosis include:

  • Feeling sick to your stomach and throwing up
  • A loss of too much body fluid (dehydration)
  • Stomach pain
  • Fruity-smelling breath
  • Trouble breathing
  • Your heart beats too fast
  • Confusion
  • You faint or black out

DKA is an emergency and can trigger a coma or death. Go to a hospital right away if you notice any symptoms.

You're more likely to have hyperglycemia if you:

  • Don't take enough insulin or other diabetes medicines
  • Don't inject insulin the right way or use expired insulin
  • Don't stick with your diabetes food plan
  • Don't stay active
  • Are sick or have an infection
  • Take medicines like steroids or those that keep your immune system in check
  • Are injured or have had surgery
  • Are stressed

Talk to your doctor about whether you should take more diabetes medicine than normal when you're ill or dealing with stress.

If you have diabetes and notice any of the early signs of high blood sugar, test your blood sugar and call the doctor. They may ask you for the results of several readings. They could recommend the following changes:

Drink more water. Water helps remove extra sugar from your blood through urine, and it helps you avoid dehydration.

Exercise more. Working out can help lower your blood sugar. But under certain conditions, it can make blood sugar go even higher. Ask your doctor what kind of exercise is right for you.

Caution: If you have type 1 diabetes and your blood sugar is high, you need to check your urine for ketones. When you have ketones, do NOT exercise. If you have type 2 diabetes and your blood sugar is high, you must also be sure that you have no ketones in your urine and that you are well-hydrated. Then your doctor might give you the OK to exercise with caution as long as you feel up to it.

Change your eating habits. You may need to meet with a dietitian to change the amount and types of foods you eat.

Switch medications. Your doctor may change the amount, timing, or type of diabetes medications you take. Don’t make changes without talking to them first.

If you have type 1 diabetes and your blood sugar is more than 250 mg/dL, your doctor may want you to test your urine or blood for ketones.

Call your doctor if your blood sugar is running higher than your treatment goals.

If you work to keep your blood sugar under control – follow your meal plan, exercise program, and medicine schedule – you shouldn’t have to worry about hyperglycemia. You can also:

  • Know your diet – count the total amounts of carbs in each meal and snack.
  • Test your blood sugar regularly.
  • Tell your doctor if you have repeated abnormal blood sugar readings.
  • Wear medical identification to let people know you have diabetes in case of an emergency.

Living with hyperglycemia can mean other health problems, some that mean you need help right away and others that you may live with for the rest of your life. 

Long-term health problems
Untreated hyperglycemia can trigger other long-term health problems, such as:

  • Diseases of the heart and blood vessels (cardiovascular disease)
  • Nerve damage (neuropathy)
  • Kidney damage (diabetic nephropathy) or kidney failure
  • Blood vessel damage in your eyes (diabetic retinopathy)
  • Poor blood flow or damage to the nerves leading to your feet, causing possible skin infections, ulcers, and the loss of your feet (amputation)
  • Issues with your bones and joints
  • Infections of your teeth and gums

Emergency health problems
Some conditions caused by blood glucose levels that are too high need treatment right away:

  • Diabetic ketoacidosis. This is when a lack of insulin, along with a high level of ketones, causes your blood to turn acidic.
  • Hyperosmolar hyperglycemic state. When your body makes insulin, but it doesn't work the right way, you may get this condition. Your blood glucose levels will then rise higher than 600 mg/dL without ketoacidosis. A hyperosmolar hyperglycemic state can make you dangerously dehydrated.

Both conditions can cause you to go into a coma, and even lead to death if they aren't treated. 


Blood sugar control is crucial in managing diabetes since high blood sugar can lead to health problems. Track your blood sugar, take insulin or other medicines as prescribed by your doctor, keep a balanced diet, stay hydrated, and exercise routinely to manage high blood sugar. If you notice symptoms of hyperglycemia, talk to your doctor about your diabetes management plan.

What are symptoms of hyperglycemia?

Symptoms of early hyperglycemia include:

  • Feeling thirsty
  • Headaches
  • Trouble focusing
  • Blurred vision
  • Peeing a lot

Does hyperglycemia turn into diabetes?

If you have hyperglycemia, this typically means you have diabetes. You may have hyperglycemia episodes a lot if you live with diabetes.