Hyperglycemia is an abnormally high level of glucose (blood sugar). It occurs when the body lacks or cannot properly use insulin. Insulin is a hormone needed to process glucose for energy.

Hyperglycemia can affect anyone with diabetes, including those individuals who are undiagnosed. Left untreated, acute hyperglycemia can lead to severe dehydration resulting in coma or death. Chronic hyperglycemia may cause complications including heart conditions, eye diseases, kidney disease (diabetic nephropathy) and nerve disease (neuropathy).

People with diabetes can often prevent hyperglycemia by following a physician-recommended management plan involving diet, exercise, and insulin or oral diabetes medication (antidiabetic agents). Patients should regularly monitor their blood glucose levels. When glucose levels are high, they should adjust their plan as advised by their physician. Despite these efforts, unexplained episodes of high blood glucose may occur.

It is essential for a person with diabetes to recognize the symptoms of hyperglycemia and know how to treat it.  People with diabetes can avoid the complications of hyperglycemia by checking their glucose levels often with a glucose meter and treating high glucose early. A physician can recommend how often a patient should test and what the target glucose range is. It is important to avoid overcompensating and developing low blood glucose (hypoglycemia), another dangerous condition.

Mild hyperglycemia can also occur in people with prediabetes, a condition in which glucose is above normal but not high enough for a diagnosis of diabetes. Lifestyle changes involving weight loss and exercise can help keep prediabetes from developing into type 2 diabetes. In some cases nondiabetics may experience hyperglycemia due to causes such as medications, heart attack, eating disorders or adrenal disease.

About hyperglycemia

Hyperglycemia is abnormally high glucose (blood sugar). High blood glucose occurs when the body lacks or cannot properly use insulin. Insulin is a hormone the body needs to process glucose for energy.

The two types of hyperglycemia are:

  • Fasting hyperglycemia. High glucose after a person has not eaten for at least eight hours.
  • Postprandial hyperglycemia. High glucose one to two hours after a person has eaten.

A certain level of postprandial hyperglycemia is a normal physiological reaction. People with and without diabetes also experience a natural early-morning rise in blood glucose. However, this state, known as dawn phenomenon, can complicate management of diabetes for some patients.

The American Diabetes Association (ADA) has established guidelines for glucose goals for people with diabetes. The guidelines list normal glucose levels for whole blood and plasma. Different tests measure glucose in different ways. Most glucose meters measure the glucose level in a blood sample as whole blood (blood with all of its components intact), whereas most laboratory tests measure the glucose in plasma (the fluid portion of the blood that contains water, minerals and proteins).

In addition, some glucose meters translate whole blood readings into plasma readings. Because plasma readings are generally 10 to 15 percent higher than whole blood glucose measurements, it is important for patients to know whether their test results are presented as whole blood or plasma measurements.

The ADA’s guidelines for blood glucose goals for people with diabetes are:  

Normal Glucose Readings
(in milligrams per deciliter)

Time of dayWhole bloodPlasma
Before meals80 to 12090 to 130
1 to 2 hours after mealsLess than 170Less than 180
Bedtime100 to 140110 to 150

These ranges, however, are not appropriate for everyone. Target glucose range is a personalized number given by a physician. It is usually based on factors such as age and the presence of diabetic complications or other medical conditions. For diabetic individuals being treated with medications such as insulin, it also considers the patient’s tendency to have hypoglycemia unawareness – a condition in which the normal symptoms associated with low blood glucose (hypoglycemia) are not felt or noticed. Patients should aim to keep their glucose levels within their personalized range.

An important supplement to regular glucose monitoring with a meter is the glycohemoglobin A1C test. This blood test, often referred to simply as an A1C test, reveals the average glucose control over the past few months.

Glycohemoglobin targets vary according to the patient’s individual needs and the physician. A goal for many people with diabetes, and one suggested by the U.S. National Institute of Diabetes and Digestive and Kidney Diseases, is a glycohemoglobin of less than 7 percent. The International Diabetes Foundation, the American College of Endocrinology and the American Association of Clinical Endocrinologists recommend a maximum of 6.5 percent for people with type 2 diabetes. However, research indicates that most Americans with type 2 diabetes have not met that goal.  

High glucose can happen to all people with diabetes, especially those who are undiagnosed. An occasional high reading is not necessarily a serious issue. Patients should discuss in advance with their physician about how to deal with hyperglycemia and at what level an episode should be reported.

When hyperglycemia is detected, it is important for people with diabetes to treat it promptly, as advised by their physician.  Severe hyperglycemia can lead to serious consequences within a short period of time, whereas hyperglycemic complications such as eye, nerve and kidney disease can take many years to develop. Potential risks of high blood glucose include:

  • Diabetic ketoacidosis (DKA). When the body lacks insulin and cannot use glucose for energy, it begins to break down fats to use for energy, producing a toxic waste product called ketones. The buildup of ketones (ketosis) in combination with hyperglycemia can escalate to life-threatening ketoacidosis.
  • Hyperosmolar hyperglycemic nonketotic syndrome (HHNS). This dangerous condition includes severe hyperglycemia and dehydration without significant ketosis.
  • Cardiovascular and other diseases. Hyperglycemia has been linked to atherosclerosis and unhealthy cholesterol levels, two major risk factors for heart disease. Hyperglycemia can also damage the blood vessels and lead to diabetic angiopathy. Angiopathy, in turn, raises the risk of diseases of the heart, brain, extremities (peripheral vascular disease), eyes (diabetic retinopathy) and kidneys (diabetic nephropathy).
  • Diabetic neuropathy. High blood glucose appears to enter into a chemical reaction with the nerves or cells around the nerves. This reaction damages the nerves, impairing transmission of signals and often causing discomfort. Hyperglycemia also damages the blood vessels that carry oxygen and nutrients to the nerves. Neuropathy linked to hyperglycemia has even been diagnosed in people with prediabetes.
  • Impaired thinking. Episodes of hyperglycemia make it harder for diabetic individuals to think quickly and solve problems, scientists have found.
  • Pregnancy complications. Maternal hyperglycemia can affect development of the fetus’ organs within the first two months, before the woman may even know she is pregnant. Control of the mother’s hyperglycemia has been shown to reduce the risk of miscarriage and birth defects.
  • Sexual dysfunction. Hyperglycemia has been found in men to increase the risk of erectile dysfunction.
  • Cancer risk. Research indicates that hyperglycemia may raise the risk of colon cancer, pancreatic cancer and possibly other cancers.
  • Interference with renal dialysis. Diabetic kidney patients undergoing dialysis have a better prognosis if their glucose is under control, scientists have found.
  • Prostate enlargement. Some research has linked hyperglycemia and obesity to greater risk of benign prostatic hyperplasia (BPH), a common noncancerous condition in middle-age and elderly men.

The U.S. Centers for Disease Control and Prevention (CDC) reported in 2006 that fatal episodes of DKA and HHNS have declined in recent decades. Researchers at the Department of Veterans Affairs, though, issued a report linking hyperglycemia with increased mortality in intensive-care patients, especially in those who were not diagnosed with diabetes but had a heart condition or stroke.

Hyperglycemia can occur in patients with diagnosed or undiagnosed prediabetes. Left untreated, glucose levels can continue to rise, causing prediabetes to develop into type 2 diabetes. However, people with prediabetes can prevent or delay the development of type 2 diabetes by making lifestyle changes involving weight loss, exercise and diet.

In some cases people without prediabetes or diabetes can experience episodes of hyperglycemia due to causes such as medications or severe stress. Prolonged exposure could lead to secondary diabetes.

Risk factors and potential causes of hyperglycemia

Many factors can alter glucose (blood sugar) levels in people with diabetes. Common triggers of high blood glucose (hyperglycemia) include:

  • Skipping or taking too little insulin or oral diabetes medication (antidiabetic agents), taking insulin or antidiabetic agents at the wrong time, or using expired or spoiled insulin.
  • Malfunction of an insulin pump, such as an obstruction in tubing.
  • Increased emotional stress.
  • Illness, infection or other physical stress.
  • Lack of exercise.
  • Overeating or eating the wrong type of food.
  • Dawn phenomenon and the Somogyi effect (rebound hyperglycemia in the morning after an overnight bout of hypoglycemia).
  • Certain medications, such as corticosteroids (an anti-inflammatory class of immunosuppressives), diuretics, beta blockers (a class of antihypertensives), antipsychotics, some antidepressants and certain antibiotics.

In some cases nondiabetics can experience hyperglycemia due to causes such as medications, intravenous glucose, severe stress (e.g., from a heart attack or stroke), eating disorders, pancreatitis, pancreatic cancer, polycystic ovarian syndrome, Cushing’s disease (overactive adrenal glands) or acromegaly (overactive pituitary gland). Where such factors are chronic, secondary diabetes may result.

Signs and symptoms of hyperglycemia

Symptoms of high glucose (blood sugar) may develop over a period of hours to days. When glucose levels are slightly elevated, the patient may have mild symptoms or no symptoms at all. As glucose levels continue to increase, some people can develop more intense symptoms. Other individuals may show no symptoms until their glucose levels are very high because their bodies adjust to the increase.

Common symptoms of hyperglycemia include:

  • Polyuria (excessive urination)
  • Polydipsia (excessive thirst)
  • Polyphagia (excessive hunger)
  • Weakness
  • Fatigue, exhaustion or lethargy
  • Blurred vision

Other signs and symptoms include:

  • Sweet, fruity-smelling breath
  • Drowsiness
  • Loss of appetite
  • Stomach pain
  • Nausea or vomiting
  • Sudden unexplained weight loss
  • Heavy labored breathing (Kussmaul breathing)
  • Dehydration
  • Dry mouth or skin
  • Slow-healing sores
  • Frequent infections, such as yeast infections or urinary tract infections
  • Difficulty concentrating
  • Headaches
  • Unconsciousness/coma

People with diabetes can avoid the advanced symptoms of hyperglycemia by checking their glucose levels often with a glucose meter and then treating high blood glucose early, according to their physician’s recommendations.

Diagnosis methods for hyperglycemia

People with diabetes can perform self-tests of hyperglycemia (high blood glucose). Also known as glucose monitoring, self-testing of glucose (blood sugar) usually involves pricking the finger for a sample of blood and placing that sample on a test strip. The strip is then analyzed by a glucose meter. The meter digitally displays the glucose level as a number in milligrams per deciliter (mg/dL).

A high blood glucose reading is any reading above a patient’s physician-recommended target range. Although other methods exist, the glucose meter is considered the most accurate home method for measuring day-to-day glucose control.

Glucose blood tests performed in healthcare settings can also detect hyperglycemia.

Although they are typically used only when blood testing is impossible, urine tests can also be used to check for hyperglycemia. Glucose is generally detectable in urine once blood glucose levels rise above 180 mg/dL, although this is highly variable.

Treatment options for hyperglycemia

Adjustments to a patient’s diabetes management plan by a physician can treat frequent or resistant high glucose (blood sugar). If behavioral changes fail to control hyperglycemia, a physician may alter the patient’s medication plan. Steps to lower blood glucose levels include:

  • Exercising. Exercise can lower glucose levels and is often a crucial part of a diabetes treatment plan. However, exercise is not recommended for a patient with ketosis, a precursor to diabetic ketoacidosis.
  • Changing eating habits. Eating too much food, too much of the wrong type of food or at the wrong time can lead to high glucose. A registered dietician can recommend dietary changes that help keep a glucose levels within a healthy range.
  • Changing insulin and antidiabetic agents. When changes in exercise and diet are not effective in lowering glucose levels, a physician may alter a patient’s type of insulin or medication, the dosage or the schedule.
  • Drinking enough water. Water aids the removal of excess glucose from the blood and can prevent dehydration. Some experts recommend drinking 8 to 12 eight–ounce glasses of water a day (1.9 to 2.8 liters). The Institute of Medicine suggests 125 ounces (3.7 liters) of water daily for men and 91 ounces (2.7 liters) for women.
  • Addressing unstable diabetes. Some cases of diabetes involve severe swings in glucose and are difficult to control. Noncompliance by the patient is often but not always a factor. The physician may recommend options such as switching to a newer glucose meter that allows continuous glucose monitoring, using an insulin pump or inhaled insulin, increasing patient and family education with a certified diabetes educator, trying newer diabetes medications such as synthetic amylin, or seeking a pancreas transplant or islet cell transplant.

In cases of hyperglycemia not involving diabetes, a physician may make recommendations such as treating any underlying condition (e.g., prescribing weight loss and ovulation drugs for polycystic ovarian syndrome) or dropping a glucose-raising drug for another medication (e.g., lowering blood pressure with an ACE inhibitor instead of a beta blocker).

Prevention methods for hyperglycemia

Practicing good diabetes management is the best way to prevent high glucose (blood sugar). Patients should follow their physician-recommended schedule of diet, exercise, insulin and oral diabetes medication (antidiabetic agents). Despite these efforts, unexplained episodes of high blood glucose (hyperglycemia) may occur.

In addition to following the treatment plan established by a physician, steps to prevent hyperglycemia include:

  • Storing insulin properly. Insulin that has been exposed to extreme heat or cold should not be used.
  • Checking the expiration date on the insulin and examining the bottle for unusual particles or crystals. Expired or spoiled insulin should not be used.
  • Carrying extra insulin pump supplies. Patients who use an insulin pump should carry extra needles, insulin, tubing, batteries and a syringe in case the pump malfunctions.
  • Exercising more. People with diabetes can sometimes reduce glucose levels with exercise. Patients should follow a physician-recommended exercise schedule and generally should avoid exercise when ketones are present in the blood or urine.
  • Eating correctly. Consistency from day to day in the timing and amount of food eaten can lead to better control over glucose. Patients should monitor their intake of starch and sugar because carbohydrates raise blood glucose levels. A registered dietician can advise a person with diabetes on healthy food choices and may suggest several small meals throughout the day instead of three large ones.
  • Using stress management techniques. 
  • Preparing for sick days. People with diabetes can counteract the rise in glucose resulting from illness, infection or other physical stress by preparing a sick- day plan with their physician ahead of time. Patients should know how and how often to perform glucose monitoring and ketone testing, what medicines to take and how to eat. Patients should also get vaccinated against pneumonia and the flu, and treat infections early.
  • Talking to a physician or pharmacist about the potential interactions and side effects of medications and supplements. For example, certain over-the-counter medications (e.g., decongestants and cough medicine) and a range of prescription drugs can raise blood glucose levels.

Questions for your doctor about hyperglycemia

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about hyperglycemia:

  1. What is my blood glucose level, and what range should I strive for?
  2. Do I have or am I at risk of developing hyperglycemia?
  3. At what point is my glucose level considered hyperglycemic?
  4. At what point do I need to report a hyperglycemic episode to you or take emergency action?
  5. How often should I check my blood sugar, and how often should I have you or another health professional check it?
  6. Is dawn phenomenon a concern for me?
  7. What are ketones? How do they interact with high glucose? When should I perform a ketone test?
  8. If ketones are present in my urine, what steps should I follow to prevent or control diabetic ketoacidosis?
  9. What can happen if I experience hyperglycemia and dehydration? How can I avoid hyperosmolar hyperglycemic nonketotic syndrome?
  10. Is it dangerous for me to have an occasional episode of hyperglycemia, or is this likely to happen and not a cause for alarm?
  11. What health risks can hyperglycemia pose for me?
  12. What are my treatment options for hyperglycemia?
  13. Can I prevent hyperglycemia?
  14. How do I avoid overcompensating and developing hypoglycemia?
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