Diabetes mellitus is a metabolic disorder characterised by hyperglycemia (high blood sugar) resulting from low levels of the hormone insulin or resistance to insulin's effects. The characteristic symptoms of diabetes are polyuria (excessive urine production), polydipsia (thirst and increased fluid intake) and blurred vision; these symptoms may be absent if the blood sugar is only mildly elevated.
Diabetes can cause many complications. Acute complications such as hypoglycemia, ketoacidosis or nonketotic hyperosmolar coma may occur if the disease is not adequately controlled. Serious long-term complications associated with diabetes include cardiovascular disease, chronic renal failure, retinal damage (which can lead to blindness), nerve damage and microvascular damage which may cause erectile dysfunction (impotence) and poor healing. Poor healing of wounds, particularly of the feet, can lead to gangrene, which may require amputation.