CLASSIFICATION
Diabetes can be classified into the following general categories:
1. Type 1 diabetes (due to b-cell destruction, usually leading to absolute insulin
deficiency)
2. Type 2 diabetes (due to a progressive insulin secretory defect on the background
of insulin resistance)
3. Gestational diabetes mellitus (GDM) (diabetes diagnosed in the second or third
trimester of pregnancy that is not clearly overt diabetes)
4. Specific types of diabetes due to other causes, e.g., monogenic diabetes syndromes
(such as neonatal diabetes and maturity-onset diabetes of the young [MODY]), diseases
of the exocrine pancreas (such as cystic fibrosis), and drug- or chemical-induced
diabetes (such as in the treatment of HIV/AIDS or after organ transplantation)
This section reviews most common forms of diabetes but is not comprehensive.
For additional information, see the American Diabetes Association (ADA) position
statement “Diagnosis and Classification of Diabetes Mellitus” (1).
Assigning a type of diabetes to an individual often depends on the circumstances
present at the time of diagnosis, with individuals not necessarily fitting clearly into a
single category. For example, some patients cannot be clearly classified as having
type 1 or type 2 diabetes. Clinical presentation and disease progression may vary
considerably in both types of diabetes.
The traditional paradigms of type 2 diabetes occurring only in adults and type 1
diabetes only in children are no longer accurate, as both diseases occur in both cohorts.
Occasionally, patients with type 2 diabetes may present with diabetic ketoacidosis
(DKA). Children with type 1 diabetes typically present with the hallmark symptoms
of polyuria/polydipsia and occasionally with DKA. The onset of type 1 diabetes may be
variable in adults and may not present with the classic symptoms seen in children.
However, difficulties in diagnosis may occur in children, adolescents, and adults, with
the true diagnosis becoming more obvious over time.