Distinguishing types of diabetes

Distinguishing the type of diabetes is based on the presenting features. See Management of first presentation of severe hyperglycaemia in adults for further information about an adult with a first presentation of severe hyperglycaemia.

Children and adolescents should be presumed to have type 1 diabetes unless proven otherwise by specialist assessment. Suspected diabetes in children and adolescents is a medical emergency; it may result in development of life-threatening complications of acute insulin deficiency, such as diabetic ketoacidosis (DKA).

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

Typically, type 1 diabetes presents acutely with recent onset of polyuria, polydipsia, and weight loss with ketosis. Type 2 diabetes has a more gradual onset and typically occurs in overweight patients with other risk factors associated with diabetes, such as dyslipidaemia and elevated blood pressure. Other typical features at initial presentation of type 1 and type 2 diabetes are listed in #dbg1-c01-s2__tdbg1-c01-tbl2.

However, the classification of diabetes is not always clear at the time of diagnosis and may only become apparent over time. Furthermore, type 1 and type 2 diabetes are heterogeneous disorders—clinical presentation and disease progression can vary considerably. For example:

  • Although type 1 diabetes most commonly presents in children and adolescents, it can present at any age.
  • Excess weight does not necessarily indicate type 2 diabetes—approximately one-quarter of patients with type 1 diabetes are overweight at diagnosis.
  • DKA is typically considered a hallmark in the diagnosis of type 1 diabetes, but it can also occur in type 2 diabetes (although uncommon).
  • A small proportion of patients with type 1 diabetes do not have autoantibodies associated with type 1 diabetes, so type 1 diabetes (and the need for immediate insulin treatment) should not be ruled out in a patient with clinical features of but without type 1 diabetes–associated autoantibodies.
Note: Seek expert advice when the clinical picture is unclear.

Seek expert advice if the type of diabetes is not clear. Other uncommon types of diabetes or conditions causing hyperglycaemia should be suspected when:

  • the clinical picture is unusual for either type 1 or type 2 diabetes
  • a patient is not responding to treatment as expected
  • there are other features of a syndrome or alternative pathology (eg clinical features of acromegaly in a patient with hyperglycaemia).

However, routine testing for uncommon types or causes of diabetes is not recommended.

Note: Routine testing for uncommon types or causes of diabetes is not recommended.