Medically reviewed by Carina Fung, PharmD, BCPPS

What is hyperglycemia?

Hyperglycemia1 is the condition that occurs when the body’s blood glucose (blood sugar) levels are too high. The term “hyperglycemia” originates from the combination of three Greek words: hyper (“high”), glykys (“sweet”), and haima (“blood”).

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Hyperglycemia can develop when the body either doesn’t produce enough insulin or doesn’t use insulin correctly. The condition is characterized by blood glucose levels higher than 125 mg/dL before a meal (fasting) and greater than 180 mg/dL two hours after eating. If a person has borderline blood glucose levels (just below hyperglycemic), they may be diagnosed as prediabetic.

While every person who has been diagnosed with diabetes mellitus (DM, or diabetes) experiences hyperglycemia, not all people with hyperglycemia are diabetic. Additionally, people with diabetes can experience changes in blood sugar levels due to changes in factors like exercise, food choices, illness, taking medications unrelated to diabetes, and not taking enough glucose-controlling medications.

Hyperglycemia can be harmful if left untreated for long periods of time. Untreated hyperglycemia can result in damage to the nerves, blood vessels, and other organs in the body (such as the eyes and heart). Because of this, prompt diagnosis and management of the condition (through monitoring blood glucose levels) are extremely important.

Hypoglycemia vs. hyperglycemia

These conditions can be thought of as opposites: hypoglycemia2 occurs when one’s blood sugar levels are too low, while hyperglycemia3 occurs when one’s blood sugar levels are too high. People with diabetes mellitus (DM) can develop hyperglycemia if their diabetes is not properly controlled.

Hypoglycemia is most common in people who take insulin injections or use other types of medication to lower their blood sugar. Low blood sugar, also known as an insulin reaction or insulin shock, is categorized as less than 70 mg/dL (or any level that requires medical intervention to bring it back up to a normal range).

The primary cause of low blood sugar is an excess of insulin, the hormone that controls blood glucose levels. While it is more common for people with type 1 diabetes to experience hypoglycemia, the condition can also be seen in those with type 2 diabetes. Noticeable symptoms of hypoglycemia—such as feeling faint, nauseous, shaky, lightheaded, or dizzy—don’t generally occur until blood glucose levels drop below 70 mg/dL.

In some cases, people may experience hypoglycemia but may not feel any symptoms. This condition, known as hypoglycemia unawareness, can pose a severe health risk if left untreated. People with known hypoglycemia unawareness should check their blood sugar more frequently, especially before performing critical tasks like operating a vehicle.

Nondiabetic hyperglycemia

Hyperglycemia can occur in nondiabetic people in one form of the condition known as stress induced hyperglycemia4 (SIH, also known as stress hyperglycemia). SIH has mainly been studied in relation to patients who are critically ill or who have undergone traumatic experiences. Elevated blood glucose levels following a traumatic injury should be monitored closely, as hyperglycemia has been associated with an increased incidence of mortality (death).

People without diabetes who are chronically stressed may also develop hyperglycemia. This is because certain hormones that are released in response to stress cause a rise in blood sugar. Hyperglycemia that occurs in people without diabetes is known as transient hyperglycemia.

How common is hyperglycemia?

Hyperglycemia has become more prevalent5 over the past twenty years as a result of decreased activity levels, increased incidence of obesity, and an increasingly older population. The Centers for Disease Control and Prevention (CDC) estimate that 30.5 million people in the United States have diabetes, while almost 84 million have prediabetes.

Men and women develop hyperglycemia at equal rates. Some countries tend to have higher rates of hyperglycemia than others, such as the United States, China, India, Brazil, and Russia. Research has also shown an association between low- and medium-income households and hyperglycemia.

Hyperglycemia causes

Hyperglycemia is caused6 by the misuse or absence of insulin in the body, the reduced use of glucose, and an increased production of glucose.

When the body digests food, it breaks down carbohydrates into sugar molecules, one of which is glucose. Glucose, a primary source of energy in the body, is absorbed into the bloodstream after meals.

As glucose levels increase in the blood, the pancreas is signaled to release insulin, the hormone that helps glucose enter the cells of the body’s tissues and organs. Glucose must enter the body’s cells in order to properly perform normal cellular processes. Excess glucose that isn’t absorbed by these cells travels to the liver and muscles to be stored as glycogen.

As glucose enters the cells and is stored in the liver and muscles, the amount that remains in the bloodstream is reduced. Once the body has restored the normal balance of blood glucose levels, it reduces insulin production, as well.

In people with diabetes, the effect of insulin in the body is lowered. People with type 1 diabetes cannot produce insulin, while those with type 2 diabetes are either resistant to insulin’s effects or do not produce adequate amounts to modulate their blood glucose. Diabetics are very likely to develop hyperglycemia, as this condition causes blood glucose to tend to accumulate in the bloodstream.

Hyperglycemia may result from secondary causes as well, including:

  • Pancreatic damage or cancer
  • Endocrine disorders such as Cushing syndrome, acromegaly, and pheochromocytoma
  • Taking medications such as exogenous estrogen or glucocorticoids
  • Gestational diabetes (high blood sugar levels during pregnancy)
  • Trauma or critical illness

Risk factors for hyperglycemia

Hyperglycemia is associated with a number of risk factors7 (factors that can increase your chances of developing the condition), including:

  • Being overweight or obese (specifically, having a body mass index, or BMI, between 25 and 30)
  • Having a family history of hyperglycemia or Type 2 diabetes
  • Having a history of gestational diabetes
  • Belonging to certain ethnic groups such as Native Americans, Hispanics, Asian Americans, African American, or Pacific Islanders
  • Having polycystic ovarian syndrome (PCOS)
  • Misusing or not using enough insulin or diabetes medication
  • Having inadequate levels of physical activity
  • Being emotionally stressed
  • Eating foods that do not align with an ideal diet for managing diabetes

People with diabetes may need to take additional medication to control their blood sugar during periods of stress or while ill in order to prevent developing hyperglycemia.

Hyperglycemia symptoms

Hyperglycemia does not typically manifest symptoms until blood glucose (sugar) levels are already elevated above the normal threshold. This occurs at about 180-200 mg/dL. The symptoms of hyperglycemia don’t generally arise suddenly. Rather, symptoms usually start to develop slowly and take days or weeks to become noticeable.

Early symptoms8 of hyperglycemia may include the following9:

  • Increased thirst
  • Frequent urination
  • Cuts or sores that heal more slowly than normal
  • Vaginal or skin infections
  • Increased hunger
  • Numb or tingling feet
  • Blurry vision
  • Fatigue or tiredness
  • Headache

If hyperglycemia is not treated properly, it can lead to serious complications, such as a toxic buildup of acid in the blood and urine (known as ketoacidosis). Other advanced symptoms of hyperglycemia may include the following10:

  • Breath with a fruity odor
  • Nausea
  • Vomiting
  • Difficulty catching your breath
  • Dry mouth
  • Muscle weakness
  • Abdominal pain
  • Confusion
  • Coma

Hyperglycemia complications

If not treated properly, hyperglycemia can result in a variety of complications. Some complications are considered long-term (chronic), while others may be acute (short-lived) and urgent.

Long-term complications11 of hyperglycemia include:

  • Heart disease
  • Nerve damage or nerve pain (diabetic neuropathy)
  • Kidney damage or failure
  • Blood vessel damage, particularly to the vessels in the retina (which can lead to a condition known as diabetic retinopathy)
  • Clouding of vision or cataracts
  • Poor blood flow to the feet, potentially leading to ulcers and other infections
  • Joint and bone issues
  • Gum infections

Acute or emergency complications12 that may result from hyperglycemia include:

  • Diabetic ketoacidosis: When the body doesn’t produce sufficient insulin, blood sugar levels rise, and the body begins to use fat for energy. This process of breaking down this fat leads to the production of ketones in the blood, which can overflow to the urine. If this acute condition is not noticed quickly, a person may enter a diabetic coma and be at risk of death.
  • Hyperglycemic hyperosmolar state: This acute condition can occur when the body fails to use insulin properly, leading to blood glucose levels of over 1,000 mg/dL. When this happens, glucose begins to collect in the blood and overflows to the urine, leading to increased urination. This can cause life-threatening dehydration and, in some cases, coma.

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