Whenever you bite into a piece of fruit or eat a bowl of pasta, you’re providing your body with the energy and nutrients it needs to stay healthy. One of the most important nutrients is glucose, a type of sugar. It‘s a main source of energy, and it travels in the bloodstream to cells throughout your body.

Normally, our bodies carefully regulate glucose levels, making sure they don’t get too high or too low. But sometimes, as happens in people with diabetes, the body is unable to effectively control those levels. Hyperglycemia occurs when the level of blood glucose gets too high.

Hyperglycemia can affect people of any age and can cause a range of symptoms, including excessive thirst, hunger, fatigue, and/or an urge to urinate larger amounts than usual. If left untreated for a long period of time, it can lead to serious complications, such as eye damage, kidney problems, and heart disease, among others. Fortunately, treatments are available that can help prevent hyperglycemia and control blood glucose levels.

Hyperglycemia is a condition in which the level of glucose in the blood is higher than normal. Sometimes called “high blood sugar,” it commonly affects people who have diabetes mellitus, but it can also develop in non-diabetics.

Glucose is the primary source of energy for all cells in our bodies. It comes from the foods we eat, especially carbohydrates. When food reaches the stomach, it is broken down into different parts—one of which is glucose. The intestines absorb the glucose, which then enters the bloodstream and circulates around the body.

Normally, the body uses a hormone called insulin to move glucose from the blood into cells, thereby lowering glucose in the blood and providing cells with energy.

Hyperglycemia can occur when the body does not produce enough insulin or does not respond to insulin correctly. In both cases, glucose stays in the blood instead of being sent to the cells, and as a result, blood glucose levels remain elevated. If more glucose enters the bloodstream—if you eat carbohydrate-rich food, for example—the blood glucose levels climb even higher.

In some cases, people with diabetes who have hyperglycemia can develop a complication called diabetic ketoacidosis (DKA). In this condition, the cells cannot access glucose. Instead, the body gets energy by breaking down fats. This process produces compounds called ketones, which build up in the blood, causing it to become acidic. DKA is a life-threatening condition. (DKA is most commonly associated with type 1 diabetes, but can occur in people with type 2 as well.)

In people with type 2 diabetes, very high blood glucose levels can lead to a life-threatening condition called hyperosmolar hyperglycemic state (HHS), which causes profound dehydration and a change in mental status.

Hyperglycemia most commonly affects people who have diabetes. In type 1 diabetes, the body does not make enough insulin. In type 2 diabetes, the body makes an adequate amount of insulin, but the cells do not respond to it properly. This is called insulin resistance.

For people with diabetes, hyperglycemia can be triggered by:

• Eating too many carbohydrates
• Not exercising enough
• Not taking enough insulin medication (for type 1 diabetes) or other medications that regulate blood glucose levels

Hyperglycemia can also be caused by:

• Medications such as corticosteroids, thiazide diuretics, beta-blockers, and antipsychotics
• Certain conditions that affect the pancreas, which produces insulin
• Medical conditions that can cause insulin resistance, such as Cushing’s syndrome and acromegaly
• Pregnancy
• Stress

Certain factors or conditions increase the risk for hyperglycemia, including:

• Obesity or being overweight
• Family history of type 2 diabetes
• Personal history of gestational diabetes
• Prediabetes (when blood glucose levels are high, but not high enough to be diagnosed as diabetes)

Symptoms of hyperglycemia include:

• Urinating large amounts
• Excessive thirst
• Feeling tired
• Frequent hunger
• Dry mouth
• Weight loss
• Blurred vision
• Recurrent infections (e.g., urinary infections, skin infections)
• Wounds (cuts, scrapes) that heal slowly

In addition to the symptoms of hyperglycemia, people with DKA may also experience:

• Deep, rapid breathing
• Fruity-smelling breath
• Headache
• Nausea and vomiting
• Stomach pain
• Change in mental status
• Loss of consciousness, coma

HHS can cause the following symptoms:

• Dehydration
• Change in mental status
• Loss of consciousness, coma

A diagnosis of hyperglycemia usually involves a review of your medical history, a physical exam, and blood tests.

The doctor will ask about your symptoms and whether you have a family history of diabetes or other risk factors associated with hyperglycemia. He or she will conduct a physical exam.

Ultimately, though, blood tests that measure blood glucose levels are necessary to definitively diagnose hyperglycemia. For what’s called a “fasting blood glucose” (FBG) test, you will need to abstain from eating for 8 hours prior to the test. Other blood tests may include a hemoglobin A1C test (also known as glycated hemoglobin test) and an oral glucose tolerance test (OGTT).

The treatment depends on the cause of hyperglycemia, and may include the following:

• Insulin. For people with type 1 diabetes, insulin is the main treatment for hyperglycemia. In some cases, it may also be used to treat people with type 2 diabetes.
• Glucose-lowering medications. Various drugs such as metformin may be used to lower blood glucose levels.
• Glucose monitoring. People with diabetes should monitor their blood glucose levels as instructed by their doctor.
• Lifestyle changes. People with diabetes can reduce the risk of developing hyperglycemia or treat existing hyperglycemia by getting regular exercise, following a nutritious diet, and maintaining a healthy weight.

DKA and HHS are medical emergencies. They are treated with intravenous fluids, electrolytes, and insulin.

In general, hyperglycemia that is transient does not cause long-term problems. But if hyperglycemia persists, it can lead to serious complications, including eye problems, kidney damage, nerve damage, and cardiovascular disease.

But with appropriate treatment and regular monitoring of blood glucose levels, people can reduce the risk of hyperglycemia, lower their chances of having serious complications, and live healthy lives.

“The Yale Diabetes Center provides individualized care for adults with hyperglycemia whether it is transient (such as medication-induced), prediabetes, or type 1 or type 2 diabetes,” says Beatrice Lupsa, MD, a Yale Medicine endocrinologist who specializes in type 1 and type 2 diabetes. “Our staff includes endocrinologists, mid-level practitioners, and a dietitian. Our multidisciplinary approach ensures people with blood glucose problems get self-management skills and knowledge to achieve and maintain long-term optimal blood glucose control. We focus on lifestyle interventions, including healthy diet and exercise. Our patients have access to the most advanced medical care, including the latest medications and technologies to prevent hyperglycemic complications and maintain better health throughout their lives.”

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