Types of Diabetes
There are four main types of diabetes: Type 1 diabetes, Type 2 diabetes, gestational diabetes mellitus, and specific types of diabetes due to other causes. 1
The Four Main Categories
Type 1 Diabetes
- Accounts for 5-10% of all diabetes cases and results from autoimmune destruction of pancreatic beta cells, leading to absolute insulin deficiency 1, 2
- Autoantibodies (GAD, IA-2, ZnT8, anti-insulin antibodies) are present in 85-90% of individuals at diagnosis 1
- Latent autoimmune diabetes of adults (LADA) is considered a form of type 1 diabetes that presents phenotypically similar to type 2 but with autoantibodies present 1
- In children, approximately half present with diabetic ketoacidosis at diagnosis, while adults may have more variable presentation and slower progression 1
Type 2 Diabetes
- Represents 90-95% of all diabetes cases, caused by progressive non-autoimmune loss of adequate insulin secretion from beta cells, frequently with insulin resistance 1, 2
- Prevalence varies significantly by ethnicity: Native Americans/Alaska Natives (15.1%), non-Hispanic African Americans (12.7%), Hispanics (12.1%), Asians (8.0%), and non-Hispanic whites (7.4%) 1
- Prevalence increases dramatically with age: 4% in ages 18-44,17% in ages 45-64, and 25% in those over 65 1
Gestational Diabetes Mellitus
- Diabetes diagnosed in the second or third trimester of pregnancy that was not clearly overt diabetes prior to gestation 1, 2
- Screening recommended for all pregnant women at 24-28 weeks using either a one-step 75-g oral glucose tolerance test or a two-step approach with 50-g non-fasting screen followed by 100-g OGTT 1
Specific Types Due to Other Causes
- Account for approximately 3-5% of all diagnosed diabetes cases 1, 2
- Monogenic diabetes syndromes include neonatal diabetes and maturity-onset diabetes of the young (MODY) 1
- Exocrine pancreatic diseases such as cystic fibrosis and pancreatitis 1
- Drug or chemical-induced diabetes from glucocorticoids, HIV/AIDS treatment, or post-organ transplantation 1
- All children diagnosed with diabetes in the first 6 months of life should have genetic testing 1
Important Clinical Distinctions
MODY Considerations
- Consider MODY in patients with mild and stable fasting hyperglycemia, stable A1C between 5.6-7.6%, multiple family members with non-typical type 1 or type 2 diabetes, and absence of obesity 1
LADA Diagnostic Approach
- When suspecting type 1 diabetes in adults, test for islet autoantibodies first (GAD as primary, followed by IA-2 and/or ZnT8 if negative) 1
- C-peptide >200 pmol/L suggests residual beta-cell function, while <200 pmol/L suggests type 1 diabetes 1
- Autoantibody testing should be prioritized when C-peptide is low-normal to avoid misdiagnosis 3
Common Pitfall to Avoid
Do not confuse diabetes mellitus with diabetes insipidus—these are completely unrelated conditions, with diabetes insipidus involving water balance and ADH rather than glucose metabolism and insulin 4