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.