Published by TDP on December 13, 2017 Diabetes mellitus occurs because of a lack of insulin or resistance to its action. It is diagnosed by measuring fasting or random blood-glucose concentration (and occasionally by glucose tolerance test). Although there are many subtypes, the two principal classes of diabetes are type 1 diabetes and type 2 diabetes. Type 1 diabetes, also referred to as insulin-dependent diabetes mellitus (IDDM), occurs as a result of a deficiency of insulin following autoimmune destruction of pancreatic beta cells. Patients with type 1 diabetes require administration of insulin. Type 2 diabetes, also referred to as non-insulin-dependent diabetes (NIDDM), is due either to reduced secretion of insulin or to peripheral resistance to the action of insulin. Although patients may be controlled on diet alone, many also require oral antidiabetic drugs or insulin (or both) to maintain satisfactory control.