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Classification of Diabetes

Newly Diagnosed | What is Diabetes? | Diabetes and Insulin | Classification of Diabetes | Diagnosis of Diabetes | Managing Diabetes | Blood Glucose Levels and HbA1c

There are many different types of diabetes resulting from various causes. The table below provides a basic classification by aetioloigy (cause).

Classification of Diabetes Mellitus
Type 1 Diabetes (T1DM) Type 1A Immune mediated Type 1B Idiopathic (much less common; aetiology not known) LADA Latent Autoimmune Diabetes in Adults	Type 1 diabetes accounts for 5-10% of cases, and results from the destruction of insulin-producing beta-cells in the pancreas. It usually results in absolute insulin deficiency. Treatment involves insulin replacement by injection or insulin pump. Visit the section “Type 1 Diabetes” for more detailed information on the management of Type 1 diabetes.
Type 2 Diabetes (T2DM)	Type 2 diabetes is the ‘lifestyle-related diabetes’ that is frequently incorrectly referred to in the news and media. Type 2 diabetes accounts for up to 90% of cases. It may be essentially insulin resistance with relative insulin deficiency, or may be predominantly an insulin secretory defect with accompanying insulin resistance… or it may be something inbetween… Management ranges from lifestyle changes through to close dietary management, daily medication, and often, eventually insulin replacement. Visit the section “Type 2 Diabetes” for more detailed information on the management of Type 2 diabetes.
Gestational Diabetes (GDM)	Defined as: Any degree of glucose intolerance that is discovered during pregnancy. Reflecting the ratio of Type 2 to Type 1 diabetes, GDM represents nearly 90% of pregnancies complicated by diabetes. Treatment is determined by immediate blood glucose levels. Visit the section ‘Women’s Pages‘ for more detailed information on the diagnosis and management of Diabetes in Pregnancy.
Type 3c Diabetes (Pancreatogenic Diabetes)	Type 3c Diabetes occurs because of a variety of exocrine pancreatic diseases with varying mechanisms of hyperglycaemia. The most commonly identified causes of Type 3c Diabetes are chronic pancreatitis, pancreatic ductal adenocarcinoma, haemochromatosis, cystic fibrosis, and previous pancreatic surgery. Treatment of Type 3c Diabetes usually involves insulin replacement by injection or insulin pump therapy, and management is similar to that of Type 1 Diabetes More on Type 3c Diabetes
Monogenic Diabetes MODY Genetic defects in insulin production Neonatal Diabetes Syndromic Monogenic Diabetes Genetic defects in insulin action	Maturity-Onset Diabetes of the Young or MODY affects 1-2% of people with diabetes, although it often goes unrecognised. MODY is caused by mutations in one of 11 different genes. The 3 main features of MODY are: Diabetes typically develops before the age of 30 Diabetes runs in families from one generation to the next Diabetes may be treated by diet or tablets and does not always need insulin treatment Research into MODY genes has proven to be a useful tool in the investigation of potential new therapies for Type 2 diabetes. More on MODY Neonatal Diabetes (NDM) is caused by mutations in one of 38 different genes) describes patients with a diagnosis before the age of six months. Syndromic Monogenic Diabetes encompasses patients where their diabetes occurs as part of a monogenetic syndrome with characteristic extra-pancreatic features (caused by mutations in one of 18 different genes). Such genetic defects in insulin action include: Type A insulin resistance Donohue syndrome (Leprechaunism) Rabson-Mendenhall syndrome Lipoatrophic diabetes
Other Specific Causes of Diabetes Endocrinopathies Drug-induced or Chemical-induced Infections Uncommon forms of immune-mediated diabetes Other genetic syndromes	This group embraces the majority of diabetes for which a specific cause is known. Treatment is usually dictated by the degree of insulin insufficiency. Endocrinopathies Acromegaly Cushing’s syndrome Glucagonoma Phaeochromocytoma Hyperthyroidism Somatostatinoma Aldosteronoma Drug / chemical-induced Vacor Pentamidine Nicotinic acid Glucocorticoids Thyroid hormone Diazoxide beta-Adrenergic agonists Thiazides Dilantin alpha-Interferon Infections Congenital rubella Cytomegalovirus Uncommon forms of immune-mediated diabetes “Stiff-man” syndrome Anti-insulin receptor antibodies Other genetic syndromes associated with diabetes Down’s syndrome Klinefelter’s syndrome Turner’s syndrome Wolfram’s syndrome Friedreich’s ataxia Huntingdon’s chorea Laurence-Moon-Biedl syndrome Myotonic dystrophy Porphyria Prader-Willi syndrome
Prediabetes	Prediabetes is the term used when a persons blood glucose levels are higher than they should be, but not high enough to meet the criteria for a diagnosis of diabetes. Prediabetes is an intermediate state between ‘normoglycaemia’ and diabetes, but the person is at a significantly increased risk of cardiovascular disease as well as progression to diabetes. More on ‘Prediabetes’
Secondary Diabetes	Secondary Diabetes is the term often used if the diabetes has arisen as a result of another condition or treatment. In many instances though, there may be an existing tendency towards diabetes anyway; drugs or diseases, a few of which are mentioned above, then effectively act as an environmental stimulus, ‘unmasking’ the diabetes. Some forms of secondary diabetes result in a lack of insulin and are similar, in many respects, to Type 1 diabetes. Others are associated with insulin resistance and show parallels with what we describe as Type 2 diabetes. With the above classification, Type 3c and many of the ‘Other Specific Forms’ could fall under the ‘Secondary Diabetes’ category.

Page last updated: Jan 2025

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Newly Diagnosed | What is Diabetes? | Diabetes and Insulin | Classification of Diabetes | Diagnosis of Diabetes | Managing Diabetes | Blood Glucose Levels and HbA1c