Hyperglycemia is high blood sugar. Hyperglycemia occurs when there is too little insulin in the body or the insulin present is not used effectively, as explained by the American Diabetes Association.
Symptoms of hyperglycemia include headaches, difficulty concentrating, increased thirst, frequent urination and fatigue, according to WebMD. Prolonged high blood sugar can lead to skin infections, nerve damage, gastrointestinal problems and damage to eyes, blood vessels and kidneys.
Hyperglycemia may be managed by taking insulin, exercising and making dietary changes, according to the American Diabetes Association. If left untreated, hyperglycemia can lead to ketoacidosis, a life-threatening condition in which the body breaks down fats and produces large amounts of ketones that accumulate in the blood.