Hyperglycemia, or high blood glucose, is a symptom that characterizes diabetes. Insufficient insulin production, resistance to the actions of insulin, or both can cause diabetes to develop.

When a person eats carbohydrates, the body breaks them down into simple sugars that enter the bloodstream. Once this occurs, the pancreas releases insulin.

Insulin is a hormone that allows the body’s cells to absorb and use sugars from the blood for producing energy.

When the body does not make any or enough insulin, or when the cells are unable to use the insulin correctly, blood sugar levels increase.

In this article, we look at the relationship between hyperglycemia and diabetes.

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People with diabetes have consistently high blood sugar and ongoing monitoring is often necessary.

People with prediabetes, in which blood sugar levels are higher than normal but not as high as they would be in diabetes, are at risk of developing diabetes.

Doctors tend to diagnose prediabetes at a fasting glucose level of 100 milligrams per deciliter (mg/dl) and diabetes at 126 mg/dl.

People with prediabetes would score 140–200 on an oral glucose tolerance test. Those with diabetes would score 200 and higher.

Diabetes causes high blood sugar levels through two possible mechanisms: insufficient insulin production in the pancreas, or resistance to the action of insulin elsewhere in the body.

In type 1 diabetes, the immune system destroys the insulin-producing cells of the pancreas. In type 2 diabetes, the body’s cells resist the action of insulin, and the pancreas does not respond appropriately. It does not put out enough insulin.

People with type 1 diabetes need to take supplementary insulin to keep their blood sugars under control. Some people with type 2 diabetes might need insulin, though they may also take noninsulin oral medications.

All people with diabetes, regardless of type, should monitor their blood sugar levels to make sure they stay within a safe range.

Several behaviors can worsen hyperglycemia in people with diabetes, such as:

  • eating too many carbohydrates
  • exercising less than usual
  • taking an insufficient amount of insulin or other diabetes medications
  • experiencing stress from either other illnesses or life events
  • undergoing treatment with other medications, such as steroids

People with diabetes may need to take extra medication to keep their blood sugar levels stable during times of illness or stress.

Dawn phenomenon, or a surge of hormones occurring roughly between 4 and 5 a.m., can also push blood sugar up. This is a cause of high blood sugars in the morning.

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Blurred vision is a symptom of severe hyperglycemia.

Hyperglycemia can be dangerous, as it often does not cause symptoms until glucose levels are very high.

People who have had type 2 diabetes for several years may not have any symptoms despite having high blood sugar. Many people have undiagnosed type 2 diabetes.

Prolonged hyperglycemia increases the risk of diabetes-related complications, such as kidney disease, eye disease, and neuropathy.

Typical signs and symptoms of hyperglycemia include:

  • frequent urination
  • increased thirst
  • increased hunger
  • blurry vision
  • weight loss
  • fatigue
  • cuts or sores that do not heal
  • high sugar levels in the urine
  • weight loss


One complication of uncontrolled diabetes is diabetic ketoacidosis (DKA). In DKA, ketones, which are waste products of the body’s breakdown of fats, build up in the blood.

Ketoacidosis develops in response to an inability to use existing glucose in the bloodstream. Without insulin, or if the body is highly resistant to insulin, the body is unable to use sugar as energy.

This causes the breakdown of fats for energy, creating ketones as a waste product. Both resistance to insulin and a lack of insulin in the body can cause DKA.

However, the people most at risk are those with type 1 diabetes. Ketoacidosis is rare for people with type 2 diabetes, but it can occur.

DKA is a life-threatening condition and requires immediate treatment. Symptoms include:

  • fruity-smelling breath
  • nausea and vomiting
  • shortness of breath
  • dry mouth
  • weakness
  • confusion
  • coma
  • stomach pain

Another complication of uncontrolled diabetes is hyperglycemic hyperosmolar syndrome. This occurs when the blood sugar levels become very high.

Without treatment, diabetic hyperglycemic hyperosmolar syndrome can be life-threatening and lead to severe dehydration and possibly coma.

This syndrome is quite rare and usually occurs in older adults with type 2 diabetes. It is most likely to occur when people are sick and have difficulty hydrating themselves regularly.

Typically, a co-occurring illness such as infection or stroke causes hyperglycemic hyperosmolar syndrome in diabetes.

Long-term complications

Developing hyperglycemia as a result of uncontrolled diabetes can cause serious long-term complications. They may include:

  • blood vessel damage that increases the risk of heart disease and stroke
  • nerve damage
  • kidney damage or failure
  • damage to the blood vessels of the retina, potentially leading to vision loss or blindness
  • cataract, or clouding of the lens in the eye
  • foot problems that can lead to serious infections
  • bone and joint problems
  • skin problems, including infections and nonhealing wounds
  • tooth and gum infections
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A range of blood glucose tests can help a doctor diagnose diabetes.

A person can monitor their blood sugar at home with the help of a fingerstick or a continuous glucose monitoring system.

During a doctor’s visit, they may draw blood for an exact determination of a blood sugar. An A1C test is a blood test that indicates average blood sugar control during the previous 3 months.

The A1C test works by measuring the percentage of glucose in the bloodstream that has bound to hemoglobin, which is the oxygen-carrying protein in red blood cells. A score of higher than 6.5 on this test suggests the presence of diabetes.

The American Diabetes Association suggest the following blood sugar targets for most adults with diabetes who are not pregnant:

  • Before a meal: Blood sugar should be 80–130 mg/dl.
  • Around 1–2 hours after the beginning of the meal: Blood sugar should be under 160–180 mg/dl.

Ranges can vary depending on age and any underlying medical conditions, such as a heart, lung, or kidney disease. Ranges also vary for people who are pregnant or experiencing complications from diabetes.

All people with diabetes should use a glucose meter to monitor blood sugar at home and make sure they stay within their goal range. Home monitoring allows people to quickly notice any potentially harmful changes and immediately report problems to a physician.

Over-the-counter urinary ketone level test kits are also available to determine the presence of DKA.

If a person is experiencing any of the symptoms above, getting a positive test means that their body may be in the early stages of DKA, and they should consider seeking treatment immediately.

A doctor can adjust the drug regimen accordingly for a person with diabetes who is also experiencing symptoms of hyperglycemia. Doing so can return the person’s blood sugar to a safe level.

Visiting the emergency room might be necessary if certain symptoms occur or do not resolve, including:

  • symptoms that suggest DKA
  • blood sugar levels not responding to home management
  • a co-occurring illness, such as stroke


As well as talking to a doctor about managing their blood sugar levels, people can take the following steps to help avoid hyperglycemia:

  • Stay active: Regular exercise is an effective way to control blood sugar. Steady-state, cardio-type exercises tend to lower overall glucose levels better than high-intensity interval training. Take a long walk or bike ride to help the body utilize existing glucose.
  • Medication: People with diabetes should always take medication and follow the doctor’s instructions closely. They can adjust a prescription to suit the ongoing needs of the person with diabetes.
  • Eating: Doctors or dietitians can help a person with diabetes develop a healthful eating plan.
  • Managing stress: Taking steps to manage stress and illness may be an effective way to reduce stress-related blood sugar spikes.

Hyperglycemia is a key sign of diabetes, which is a serious condition.

People with diabetes must keep track of their blood sugar, stay within their target levels, follow a dedicated eating plan, exercise, and always take their medicine.

They should report any abnormal symptoms to their doctor. This can help people with diabetes prevent hyperglycemia and receive early treatment with a view to preventing long-term complications.


What is the best diet for keeping blood sugar within a normal range?


Many types of diet can benefit people with diabetes. Eating carbohydrates, for example, directly impacts blood sugars, so doctors recommend a carb-controlled diet.

Ketogenic diets have become popular, as they lead to rapid weight loss. However, they may have some negative health effects, so individuals should talk to their doctor before beginning any extreme diet.

Moderation is the best advice, with about 45 percent of a person’s calories coming from low-glycemic carbs such as legumes, whole grains such as stone-ground, whole-wheat bread, oatmeal or barley, and non-starchy vegetables and fruits.

Deborah Weatherspoon, PhD, RN, CRNA Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.

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