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)

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.