High Blood Sugar (Hyperglycemia)

Reviewed on 9/15/2022

Things to Know About High Blood Sugar (Hyperglycemia)

High blood sugar needs to be monitored through blood tests.
High blood sugar needs to be monitored through blood tests.

Whenever the glucose (sugar) level in one's blood rises high temporarily, this condition is known as hyperglycemia. The opposite condition, low blood sugar, is called hypoglycemia.

Glucose comes from most foods, and the body uses other chemicals to create glucose in the liver and muscles. The blood carries glucose (blood sugar) to all the cells in the body. To carry glucose into the cells as an energy supply, cells need help from insulin. Insulin is a hormone made by the pancreas, an organ near the stomach.

The pancreas releases insulin into the blood, based on the blood sugar level. Insulin helps move glucose from digested food into cells. Sometimes, the body stops making insulin (as in type 1 diabetes), or the insulin does not work properly (as in type 2 diabetes). In diabetic patients, glucose does not enter the cells sufficiently, thus staying in the blood and creating high blood sugar levels.

Blood sugar levels can be measured in seconds by using a blood glucose meter, also known as a glucometer. A tiny drop of blood from the finger or forearm is placed on a test strip and inserted into the glucometer. The blood sugar (or glucose) level is displayed digitally within seconds.

Blood glucose levels vary widely throughout the day and night in people with diabetes. Ideally, blood glucose levels range from 90-130 mg/dL before meals, and below 180 mg/dL within 1-2 hours after a meal. Adolescents and adults with diabetes strive to keep their blood sugar levels within a controlled range, usually 80-150 mg/dL before meals. Doctors and diabetes health educators guide each patient to determine their optimal range of blood glucose control.

When blood sugar levels remain high for several hours, dehydration and more serious complications can develop. Moreover, even mild hyperglycemia (a fasting blood sugar over 109 mg/dL in adolescents/adults or over 100 mg/dL in children before puberty) -- when unrecognized or inadequately treated for several years -- can damage multiple tissues in the brain, kidneys, and arteries. When hyperglycemia is associated with the presence of ketones in the urine, this state demands immediate medical attention. When blood sugar levels rise and stay high (over 165 mg/dL consistently) for days to weeks, diabetes should be suspected and treatment initiated.

High blood sugar level fluctuations occur daily in people with diabetes. It is important to control blood sugar levels through diet, exercise, and medication (if prescribed), to know the symptoms of elevated blood sugar, and to seek treatment, when necessary.

High Blood Sugar Causes

Diabetes mellitus is one of several persistent conditions causing high blood sugar levels. For someone with diabetes, hyperglycemia has many possible causes:

  • Carbohydrates: Eating food containing too many carbohydrates, a form of sugar. The body of a person with diabetes cannot process high levels of carbohydrates fast enough to convert it into energy. Blood sugar levels in patients with diabetes can rise within hours after eating.
  • Insulin control: Not producing enough insulin action (either by injection of insulin or taking medicine which stimulates the pancreas to make more insulin). People with diabetes must control blood sugar by a combination of dietary discretion, taking medication, and physical activity. When food, exercise, and insulin are not balanced, blood sugar levels rise.
  • Stress: Emotions can play a role in causing hyperglycemia, but should not be used as an excuse for poor control of diabetes.
  • Low levels of exercise: Daily exercise is a critical contributor to regulating blood sugar levels.
  • Infection, illness, or surgery: With illness, blood sugar levels tend to rise quickly over several hours.
  • Other medications: Certain drugs, especially steroids, can affect blood sugar levels.

High Blood Sugar Symptoms and Signs

A high blood sugar level itself is a symptom of diabetes. However, an individual experiencing hyperglycemia may have no symptoms at all.

Common symptoms and signs can include the following:

If hyperglycemia persists for several hours and leads to dehydration, other symptoms may develop, such as...

  • Difficulty breathing
  • Dizziness upon standing
  • Rapid weight loss
  • Increased drowsiness and confusion
  • Unconsciousness or coma

Left untreated, hyperglycemia can lead to a condition called ketoacidosis, also known as diabetic ketoacidosis (DKA) or diabetic coma. This occurs because the body has insufficient insulin to process glucose into fuel, so the body breaks down fats to use for energy. When the body breaks down fat, ketones are produced as byproducts. Some ketones are eliminated via the urine, but not all. Until the patient is rehydrated, and adequate insulin action is restored, ketones remain in the blood. Ketones in the blood cause nausea, headache, fatigue, or vomiting.

Ketoacidosis is life-threatening and demands immediate treatment.

Symptoms of ketoacidosis are as follows:

  • Shortness of breath
  • Nausea and vomiting
  • Dry mouth
  • Breath that smells fruity
  • Stomach pain

When to Seek Medical Care for High Blood Sugar (Hyperglycemia)

If hyperglycemia persists for at least two or three days, or if ketones appear in the urine, call a doctor.

Generally, people with diabetes should test their blood sugar levels at least four times a day: before meals and at bedtime (or following the schedule advised by the prescribed individual diabetes care plan). The urine should be checked for ketones any time the blood sugar level is over 250 mg/dL.

When blood sugar stays high despite following a diabetic diet and plan of care, call the nurse, diabetes health educator, or physician for adjustments in the diet.

If blood sugars are high because of illness, check for ketones and contact a health professional.

Seek immediate medical care for these conditions:

  • Vomiting
  • Confusion
  • Sleepiness
  • Shortness of breath
  • Dehydration
  • Blood sugar levels that stay above 160 mg/dL for longer than a week
  • Glucose readings higher than 300 mg/dL
  • The presence of ketones in the urine

Ketoacidosis or diabetic coma is a medical emergency. Call 911 for emergency transport to a hospital or similar emergency center.

Questions to Ask Your Doctor About High Blood Sugar (Hyperglycemia)

Please ask your health care professional about the following:

  • How to recognize high blood sugar levels
  • How to treat a high blood sugar level when it occurs in you, a family member, or coworkers
  • How to prevent the blood sugar level from becoming too high
  • How to contact the medical staff during an emergency
  • What emergency supplies to carry to treat high blood sugar
  • Additional educational materials regarding high blood sugar

Self-Care at Home for High Blood Sugar (Hyperglycemia)

Check blood sugar levels with a blood glucose meter. If the blood sugar level is higher than normal, but there are no symptoms, continue routine care such as...

  • Take all diabetes medications on schedule.
  • Eat regular meals.
  • Drink sugar-free and caffeine-free liquids.
  • Take a blood sugar reading every four hours (write it down) until levels are back to normal.
  • Check urine for ketones (all patients with diabetes) and write down the readings. Follow sick day rules as defined in your diabetes care plan until ketones disappear from urine.

The following strategies lower blood sugar levels:

  • Exercise: A simple way to lower high blood sugar is to exercise. But if blood glucose levels are higher than 240 mg/dL, first check the urine for ketones. If ketones are present, do not exercise. The risk is that blood sugar levels will rise even higher. Talk with the doctor about a safe way to lower blood glucose levels in this situation.
  • Diet: Work with a diabetes health educator or registered dietitian to develop a workable diet plan to manage diabetes.
  • Medication: If diet and exercise are not keeping blood sugar levels in the normal range, the doctor may adjust the amount, timing, or type of medications or insulin.

High Blood Sugar Treatment

  • Medication change: High blood sugars may be a sign that the person with diabetes needs to take medication, to change medications, or to change the way it is given (for example, additional insulin would be given, or a switch might be made from oral medication to injected medication).
  • Other illness: Other illnesses need to be diagnosed and treated if an illness is causing high blood sugar levels. Infection or illness may need to be treated in the hospital, where health professionals can adjust the plan of care.
  • Other Medications: A number of medications are available to help control blood sugar levels for people with type 2 diabetes. Insulin is also prescribed  for people with diabetes (all with type 1 diabetes and many with type 2 diabetes).

High Blood Sugar (Hyperglycemia) Follow-up

Patients with diabetes should have a hemoglobin A1c test performed every 3 months. Similar to a report card, this test provides feedback about the overall sugar levels for the past 3 months. People with diabetes should have a hemoglobin A1c level less than 7% at each clinical visit. Levels above 7% usually result from a person's consistent failure to

  • follow a proper plan of diet,
  • take the necessary medication(s),
  • closely monitor blood glucose, or
  • exercise.

High Blood Sugar (Hyperglycemia) Prevention

  • Learn about managing diabetes.
  • Work with a certified diabetes educator. This person will have a CDE certification and may work in a diabetes education center or hospital.
  • Check blood sugar as directed by a CDE and doctor or nurse.
  • Know the symptoms and act quickly before blood sugars get out of control.
  • Follow a diabetes diet plan. Adjust the plan as needed.
  • Take medications for diabetes as directed by your health care professional.
  • Exercise daily.

Support Groups and Counseling for High Blood Sugar (Hyperglycemia)

You or family members may wish to join a support group with other people to share your experiences. The American Diabetes Association and the Juvenile Diabetes Research Foundation are both excellent resources. Your health care provider will have information about local groups in your area. The following groups also provide support:

American Association of Diabetes Educators
100 W Monroe, Suite 400
Chicago, IL 60603
(800) 338-3633

American Diabetes Association
1701 North Beauregard Street
Alexandria, VA 22311
(800) DIABETES (342-2383)
[email protected]

American Dietetic Association
120 South Riverside Plaza, Suite 2000
Chicago, IL 60606-6995
(800) 877-1600

Juvenile Diabetes Research Foundation International
120 Wall Street
New York, NY 10005-4001
(800) 533-CURE (2873)
[email protected]

National Diabetes Education Program
One Diabetes Way
Bethesda, MD 20814-9692
(800) 438-5383
[email protected]

Reviewed on 9/15/2022
Hirsch, Irl B., and Michael Emmett. "Diabetic ketoacidosis and hyperosmolar hyperglycemic state in adults: Clinical features, evaluation, and diagnosis." UpToDate.com. July 27, 2022. <https://www.uptodate.com/contents/diabetic-ketoacidosis-and-hyperosmolar-hyperglycemic-state-in-adults-clinical-features-evaluation-and-diagnosis>.