Hyperglycemia is a symptom and cause of diabetes in which there are elevated levels of blood sugar, or glucose, in the bloodstream. In both Type I and Type II diabetes, hyperglycemia results from a complication with insulin, the chemical that lets cells get energy from glucose. Hyperglycemia causes mild to severe symptoms and can eventually lead to coma and death. It's treated by carefully monitored blood glucose levels, insulin injections, exercise, a proper diet, and oral medication.

The most common symptoms of hyperglycemia include repeated urination, hunger even after eating, and increased thirst. Secondary symptoms might be dry mouth and skin due to dehydration, low energy, or a drop in weight. Some circumstances exacerbate hyperglycemia, such as a diet rich in sugars, no exercise, stress, illness, and surgery. Hyperglycemia can be detected by measuring sugar levels in blood and urine, which might lead to a diagnosis of diabetes.

Diabetes is closely related to hyperglycemia. In Type I diabetes, the pancreas doesn't secret enough insulin to process all the glucose, so too much circulates in the bloodstream. Cells do not respond to the insulin-bonded glucose to receive energy in Type II diabetes, also resulting in elevated glucose levels. Although they have the same effect, these different kinds of hyperglycemia must be approached differently.

Standard treatment of Type I diabetes is an insulin regimen, whereby the patient injects him or herself with insulin since their body doesn't produce enough. These regular insulin injections are balanced with frequent checking for hyperglycemia with a home device. Some mild cases of diabetes can be controlled with a balanced diet, regular and vigorous exercise, and weight loss. Type II diabetes might not respond to insulin, so oral medication is prescribed along with lifestyle changes.

If left untreated or undiagnosed, rampant hyperglycemia will lead to a condition called ketoacidosis. Eventually, the body urgently needs energy. First, it will shut down lower priority functions to conserve energy, resulting in blurred vision, confused thinking, and dizziness. Then it will use fat as an energy source, rather than glucose. The body isn't designed to break down fat rapidly, so waste chemicals called ketones build up. When a critical amount of ketones are present in the blood, they poison the body and will cause an acute coma or death.