Diagnosis of Type 1 Diabetes
Diagnostic Criteria
- The American Diabetes Association recommends using plasma glucose rather than HbA1c to diagnose the acute onset of type 1 diabetes in individuals with symptoms of hyperglycemia 2
- Fasting plasma glucose (FPG) ≥126 mg/dL (7.0 mmol/L), with fasting defined as no caloric intake for at least 8 hours, is a diagnostic criterion for type 1 diabetes 3
- 2-hour plasma glucose ≥200 mg/dL (11.1 mmol/L) during an oral glucose tolerance test (OGTT) using 75g of anhydrous glucose is a diagnostic criterion for type 1 diabetes 3
- Random plasma glucose ≥200 mg/dL (11.1 mmol/L) in patients with classic symptoms of hyperglycemia or hyperglycemic crisis is a diagnostic criterion for type 1 diabetes 3
Autoantibody Testing
- The American Diabetes Association recommends measuring pancreatic autoantibodies to confirm the autoimmune nature of type 1 diabetes 2
- Key autoantibodies to test include: Islet cell autoantibodies (ICA), Glutamic acid decarboxylase autoantibodies (GAD65), Insulin autoantibodies, Tyrosine phosphatase autoantibodies (IA-2 and IA-2β), and Zinc transporter 8 autoantibodies (ZnT8) 2
- The presence of one or more of these autoimmune markers defines type 1 diabetes 2
Beta-Cell Function Assessment
- C-peptide levels should be measured to assess beta-cell function, with low or undetectable levels characteristic of type 1 diabetes 4
Special Considerations
- Approximately one-third of type 1 diabetes patients present with diabetic ketoacidosis (DKA) at diagnosis, and testing for ketones in blood or urine should be performed when type 1 diabetes is suspected 2, 4, 5
- Screening for type 1 diabetes risk with a panel of autoantibodies is currently recommended only in research settings or for first-degree family members of individuals with type 1 diabetes 2
- Persistence of two or more autoantibodies predicts clinical diabetes and may serve as an indication for intervention in clinical trial settings 2