Diabetes (mellitus) is a group of metabolic diseases characterized by elevated blood glucose levels over a longer period.

The two major types of diabetes are (1) type 1 diabetes (formerly called juvenile diabetes) in which insulin production is reduced or absent, and (2) type 2 diabetes characterized by insulin resistance.

Given these major differences between type 1 and type 2 diabetes, it is important to accurately distinguish between the two conditions.

A key finding in the characterization of type 1 diabetes as an autoimmune disease was the discovery of islet cell autoantibodies, including antibodies against (1) insulin (IAA), (2) glutamic acid decarboxylase (GADA), (3) islet-antigen 2 (IA-2), and (4) the zinc transporter protein ZnT8.

Therefore, islet cell autoantibody measurement may be used to establish the diagnosis of type 1 diabetes.

Islet cell autoantibodies may also be useful to (1) study the natural history of pre-type 1 diabetes, (2) identify individuals at risk of diabetes development, for instance amongst relatives, and (3) identify a condition known as LADA (latent autoimmune diabetes in adults) in patients with apparent type 2 diabetes.