Diabetic hyperglycemic hyperosmolar coma is a condition of decreased consciousness, extreme dehydration (lack of water), and extremely high blood glucose (sugar) levels, which is not accompanied by ketoacidosis.

The condition is usually seen in people with non-insulin-dependent diabetes (type 2 diabetes) and may occur in those previously undiagnosed with diabetes or in those who have improperly managed their medications and diet. The condition may be brought on by an infection or by certain medications that impair glucose tolerance or increase fluid loss.

Normally, the kidneys compensate for high glucose levels in the blood by excreting excess glucose in the urine. However, when water is scarce, the kidneys conserve fluid, and glucose levels become higher. This results in greater need for water.

Hyperosmolarity is a condition in which the blood is concentrated with sodium, glucose, and other molecules that normally attract water into the bloodstream. When the kidneys are conserving water, however, this creates a vicious cycle of increasing blood-glucose levels and increasing dehydration.