What is Type 4 Diabetes?
"Type 4 diabetes" is not a recognized classification in any major diabetes guideline; the term has been used informally in research literature to describe glaucoma as "brain-specific diabetes" but has no clinical validity or diagnostic criteria in standard medical practice. 1
Established Diabetes Classification
The American Diabetes Association and other major guideline bodies recognize only the following categories of diabetes: 1
- Type 1 diabetes – autoimmune β-cell destruction causing absolute insulin deficiency 1
- Type 2 diabetes – progressive β-cell insulin secretion loss with insulin resistance 1
- Gestational diabetes mellitus – diabetes diagnosed in the second or third trimester of pregnancy 1
- Specific types due to other causes – including monogenic diabetes syndromes (neonatal diabetes, MODY), diseases of the exocrine pancreas (cystic fibrosis, pancreatitis), and drug-induced diabetes 1
The "Four Types" Terminology in Literature
Some classification systems have described diabetes as having "four types," but this refers to the four categories listed above (Type 1, Type 2, Gestational, and Other specific types), not a distinct entity called "Type 4 diabetes." 1
Prediabetes is Not Type 4
Prediabetes is explicitly defined as a separate condition characterized by impaired glucose tolerance or fasting glucose that does not meet diabetes diagnostic thresholds, leading to higher risk of developing Type 2 diabetes—it is not classified as a diabetes type. 1
Pancreatic Diabetes (Type 3c)
The term "Type 3c diabetes" has been used to describe pancreatic diabetes (pancreoprivic diabetes), which results from structural and functional loss of insulin secretion in the context of exocrine pancreatic dysfunction. 1, 2 This terminology is also not universally adopted, with "pancreatic diabetes" or "diabetes in the context of disease of the exocrine pancreas" being the preferred umbrella terms. 1
Non-Standard Research Usage
One research article proposed calling glaucoma "Diabetes Type 4" based on a hypothesis linking insulin dysfunction in the central nervous system to glaucoma pathogenesis. 3 This is purely theoretical research nomenclature with no acceptance in clinical guidelines or diagnostic criteria. 3
Clinical Implications
- When encountering the term "Type 4 diabetes" in clinical practice, clarify what the referring provider means, as it has no standardized definition 1
- Use only the established ADA/WHO classification system for diagnosis and documentation 1
- If a patient presents with diabetes secondary to pancreatic disease, classify it as "specific types of diabetes due to other causes" or "pancreatic diabetes," not "Type 3c" or "Type 4" 1