Diabetes mellitus (DM) is an endocrine disorder characterized by the lack or insufficient production of insulin by the pancreas.

DM has been recognized as a disease for at least two millennia, but only since the mid-1970s has there been a consensus on its classification and diagnosis.

The primary diagnostic criterion for DM is eleva­tion of blood glucose levels during fasting or at 2 hours following a meal. Normal plasma glucose val­ues for adults in the fasting state are 80 to 120 milligrams per deciliter (mg∕dL) or 4.4 to 6.7 millimoles per liter (mmol∕L). Definition of unequivo­cal DM requires a 2-hour postingestion plasma glu­cose level equal to or greater than 200 mg/dL (11.1 mmol∕L) for the appearance of classical symptoms of diabetes. These symptoms, which include excessive urination, urine containing sugar, hunger, thirst, fatigue, and weight loss, are common to all types of DM.