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Hyperglycemia: What Is High Blood Sugar?

Symptoms, Treatments, and Prevention

Hyperglycemia means high glucose (hyper- + glyc-) in the blood (-emia). Your body needs glucose to properly function. Your cells rely on glucose for energy. Hyperglycemia is a defining characteristic of diabetes — when the blood glucose level is too high because the body isn't properly using or doesn't make the hormone insulin. Over time, hyperglycemia can lead to potentially dangerous complications. Here's a closer look at this condition, beginning with what glucose is and does in the first place. 

You may become hyperglycemic if your blood glucose is too high


What Is Glucose?

Glucose is a simple sugar your body makes from the foods you eat. The function of glucose is to provide fuel for the body. Your cells use glucose to make energy, which is the main function of sugar in the body. 

Carbohydrates, such as fruit, milk, potatoes, bread, and rice, are the biggest source of glucose in a typical diet. Your body breaks down carbohydrates into glucose sugar, and then transports this sugar to your cells via the bloodstream. “Blood sugar” just another way of saying glucose.

The Role of Insulin

In order to use glucose properly, your body needs insulin. This is a hormone produced by the pancreas. Insulin helps transport glucose into the cells, particularly the muscle cells.

People with type 1 diabetes no longer make insulin to help their bodies use glucose, so they have to take insulin, which is injected under the skin. People with type 2 diabetes may have enough insulin, but their body doesn't use it well; they’re insulin resistant. Some people with type 2 diabetes may not produce enough insulin.

People with diabetes may become hyperglycemic — that is, develop high blood sugar — if they don't keep their blood glucose level under control (by using insulin, medications, and appropriate meal planning). For example, if someone with type 1 diabetes doesn't take enough insulin before eating, the glucose their body makes from that food can build up in their blood and lead to high blood sugar.

Normal Blood Sugar Levels vs. Hyperglycemia

If you’ve been diagnosed with diabetes, your endocrinologist will tell you what your target blood glucose levels are. Your levels may be different from what is usually considered as normal because of age, pregnancy, or other factors. You will be given two target levels, or ranges, one applying to when you haven't eaten for a number of hours (fasting glucose) and one for after meals (postprandial glucose).

Fasting Glucose

This is defined as your blood sugar measurement after you haven't eaten for at least eight hours. The recommended fasting glucose range for a person without diabetes is 70 to 130mg/dL. (The standard for measuring blood glucose is "mg/dL" which means milligrams per deciliter.) If your blood glucose level after an eight-hour (or longer) fast is above 130mg/dL, that's called fasting hyperglycemia. Fasting hyperglycemia is a common diabetes complication.

Postprandial (or Reactive) Glucose

This is the level of blood sugar that occurs after you eat a meal or snack (postprandial means "after eating"). If your postprandial (1-2 hours after eating) blood glucose level is above 180mg/dL, that's postprandial or reactive hyperglycemia. During this type of hyperglycemia, your liver doesn't stop sugar production, as it normally should directly after a meal, and stores glucose as glycogen (energy sugar stores).

It's not just people with diabetes who can develop hyperglycemia. Certain medications and illnesses can cause it, including beta blockers, steroids, and bulimia. In this article, however, our focus is on hyperglycemia caused by diabetes.

Early Symptoms of Hyperglycemia

Early signs of high blood sugar, or hyperglycemia, may serve as a warning even before you test your blood glucose level. Typical high sugar symptoms may include:

  • Increased thirst and/or hunger
  • Frequent urination
  • Headache
  • Blurred vision
  • Fatigue
  • Sugar in your urine (as determined by a urine test)

It is important to recognize and treat hyperglycemia because if left untreated, it can lead to additional symptoms and complications, some of which are different for people with type 1 diabetes compared to type 2 diabetes. For example, people with type 1 diabetes are more likely to develop a severe condition resulting from high blood sugar called diabetic ketoacidosis. In addition to the common hyperglycemia symptoms listed above, symptoms of diabetic ketoacidosis (or DKA) include:

  • Heavy breathing
  • Fruity-smelling breath
  • Confusion and irritability
  • Nausea and vomiting
  • Abdominal pain

Complications of Hyperglycemia

When your blood glucose levels regularly exceed the recommended ranges (that is, when you experience hyperglycemia), it can lead to a number of long-term diabetes complications, including:

  • Eye damage
  • Heart attack or other cardiovascular problems
  • Kidney damage
  • Nerve damage
  • Stroke
  • Problems with healing wounds

Diabetic Ketoacidosis: A Complication of Severe Hyperglycemia in Type 1 Diabetes

In addition to the complications above, severe hyperglycemia in people with type 1 diabetes can lead to a dangerous condition called ketoacidosis, mentioned above. This condition develops when toxic acids called ketones build up in the blood. It can become serious and lead to diabetic coma or even death. According to the American Diabetes Association, ketoacidosis affects people with type 1 diabetes, but it rarely affects people with type 2 diabetes.

Hyperosmolar Hyperglycemic Nonketotic Syndrome (HHNS): A Complication of Severe Hyperglycemia in Type 2 Diabetes

In people with type 2 diabetes, extreme hyperglycemia (think blood glucose readings of 600 mg/dL or higher) can lead to a very rare but serious condition called hyperosmolar hyperglycemic nonketotic syndrome, or HHNS). HHNS is most likely to occur when you're sick — particularly if you aren't able to drink enough fluids or keep fluids down. It happens most often in elderly people and, like ketoacidosis, can result in a coma. 

By maintaining your blood glucose levels—and avoiding hyperglycemia—you can reduce your risk of all these complications.

Treating Hyperglycemia

If your blood glucose level is consistently too high, talk with your doctor about what you can do to keep it in a more normal range. He or she may suggest:

Medication Adjustment

Your doctor may adjust your insulin (or glucose-lowering medication) dose or when you take it to help prevent hyperglycemia.

Meal Planning Help

A healthy diet and proper meal planning can help you avoid hyperglycemia. This includes eating often, watching intake of sugar and carbohydrates, limiting use of alcohol, and eating a diet rich in vegetables, fruit and whole grains. If you are having difficulty planning meals, talk to your doctor or dietitian.


Regular exercise is important (even if you don't have diabetes). Maintaining a healthy level of activity can help you keep your blood glucose level in a normal range. However, if you develop hyperglycemia and/or ketones are present in your urine, don't exercise. Hyperglycemia and/or ketones in the urine mean exercise will cause your blood glucose to rise higher.

Preventing Hyperglycemia

The easiest way to prevent hyperglycemia is to control your diabetes. That includes knowing the early symptoms of high blood sugar, no matter how subtle, and taking steps to get your sugar back in range. Remember, there are many aspects of your diabetes care you can control:

  • Taking your insulin (or glucose-lowering medication) as prescribed
  • Avoiding consuming too many calories (i.e., sugary beverages)
  • Consuming the right types and grams of carbohydrates
  • Controlling stress
  • Staying active (exercising)
  • Going to your regularly scheduled doctor's appointments

In addition, your doctor may recommend other preventive measures to help you avoid or detect severe hyperglycemia, which can help you avoid the worst complications from it. For example, some people with diabetes are instructed by their doctor to regularly test their ketone levels. Ketone testing is performed two ways: using urine or using blood. For a urine test, you dip a special type of test strip into your urine. For testing blood ketones, a special meter and test strips are used. The test is performed exactly like a blood glucose test. If ketone testing is part of your self-monitoring of diabetes, your healthcare professional will provide you with other information. 

If you have type 2 diabetes, talk to your doctor about having a "sick day plan" for keeping your blood sugar in control on days you're under the weather, especially if you're an older adult. This can help you prevent the extreme hyperglycemia that can lead to HHNS (discussed above).

Bottom line: Hyperglycemia is a common complication of diabetes, but through medication, exercise, careful meal planning, and working closely with your doctor, you can keep your blood glucose level from running too high — and that's huge for your health in the long run.