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In addition to having elevated levels of glucose in the blood, people with hyperglycemia often have glucose detected in their urine (glycosuria). Ordinarily urine contains no glucose because it is reabsorbed by the kidneys.
Severely elevated blood sugar levels can result in a medical emergency ("diabetic coma"). This can occur in both people with type 1 and those with type 2 diabetes. People with type 1 diabetes may develop diabetic ketoacidosis (DKA), and those with type 2 diabetes can develop hyperglycemic hyperosmolar nonketotic syndrome (HHNS, also referred to as hyperglycemi hyperosmolar state). These so-called hyperglycemia crises are serious conditions that can be life threatening if not treated immediately. Hyperglycemic crises cause about 2,400 deaths each year in the U.S.
Over time, hyperglycemia can lead to damage to organs and tissues. Long-term hyperglycemia can impair the immune response, leading to poor healing of cuts and wounds. It can also cause nerve damage, vision problems, and damage to the blood vessels and kidneys (see below).
For more information, read our full medical article on hyperglycemia.
American Diabetes Association.