Classifying diabetes

Diabetes mellitus is a chronic condition caused by relative or absolute insulin deficiency. This insulin deficiency results in hyperglycaemia, which in the long term can affect many organs, in particular the blood vessels, nerves, eyes and kidneys (see Overview of complications of diabetes).

Diabetes can be classified as:

type 1 diabetes—a condition of insulin deficiency most commonly caused by immune-mediated destruction of the insulin-producing pancreatic beta cells; see type 1 diabetes in children and adolescents and type 1 diabetes in adults
type 2 diabetes—a condition of relative insulin deficiency caused by progressive loss of pancreatic beta-cell insulin secretion on a background of insulin resistance; see type 2 diabetes in children and adolescents and type 2 diabetes in adults
hyperglycaemia in pregnancy (including gestational diabetes)—diabetes first occurring or recognised during pregnancy
other types of diabetes.

For adults who present with severe hyperglycaemia, see Management of first presentation of severe hyperglycaemia in adults for immediate management, such as need for hospitalisation and the urgency of starting insulin. The priority is to address the symptoms and consequences of the hyperglycaemia, including the recognition and early management of life-threatening diabetic ketoacidosis (DKA) or hyperosmolar hyperglycaemia.

A presentation of hyperglycaemia with or without symptoms of diabetes (eg polyuria, polydipsia, weight loss) in a child or adolescent is a medical emergency. Immediate specialist assessment and management is required to avoid development of life-threatening complications of acute insulin deficiency, such as DKA. Refer the patient to the local emergency department, or phone the nearest children’s hospital or major healthcare service for specialist endocrinology advice.

Note: Suspected diabetes in children and adolescents is a medical emergency.

Children and adolescents should be presumed to have, and be treated for, type 1 diabetes unless proven otherwise by specialist assessment.

The most common types of diabetes mellitus are type 1 diabetes, type 2 diabetes and gestational diabetes. Type 1 diabetes and type 2 diabetes are heterogeneous disorders—clinical presentation and disease progression vary considerably.

Classifying the type of diabetes is important for:

helping to determine the most appropriate drug treatment—such as insulin versus other parenteral or oral antihyperglycaemic drugs
longer-term considerations—such as greater risk of other autoimmune disorders with type 1 diabetes, and of other metabolic disorders with type 2 diabetes.

See Distinguishing types of diabetes for further discussion.