From the Guidelines
Type 1 diabetes is diagnosed based on several key criteria, including a fasting blood glucose level of ≥126 mg/dL (7.0 mmol/L), a random blood glucose level of ≥200 mg/dL (11.1 mmol/L) with symptoms of diabetes, or a 2-hour plasma glucose level of ≥200 mg/dL during an oral glucose tolerance test, as well as the presence of autoantibodies such as islet cell antibodies (ICA), glutamic acid decarboxylase antibodies (GADA), insulin autoantibodies (IAA), and zinc transporter 8 antibodies (ZnT8A) 1. The primary diagnostic indicators for type 1 diabetes include:
- Persistent hyperglycemia with a fasting blood glucose level of ≥126 mg/dL (7.0 mmol/L)
- A random blood glucose level of ≥200 mg/dL (11.1 mmol/L) with symptoms of diabetes
- A 2-hour plasma glucose level of ≥200 mg/dL during an oral glucose tolerance test
- An HbA1c level of ≥6.5% (48 mmol/mol) can also support the diagnosis 1 The presence of autoantibodies such as:
- Islet cell antibodies (ICA)
- Glutamic acid decarboxylase antibodies (GADA)
- Insulin autoantibodies (IAA)
- Zinc transporter 8 antibodies (ZnT8A) are also characteristic of Type 1 diabetes 1. Low or undetectable C-peptide levels, indicating minimal endogenous insulin production, are also characteristic of Type 1 diabetes 1. The diagnosis is further supported by the typical clinical presentation, which includes the acute onset of symptoms like:
- Polyuria (excessive urination)
- Polydipsia (excessive thirst)
- Unexplained weight loss
- Sometimes diabetic ketoacidosis (DKA) 1. Type 1 diabetes typically develops in children and young adults, though it can occur at any age, and often presents more abruptly than Type 2 diabetes 1.
From the Research
Diagnostic Criteria for Type 1 Diabetes
The diagnosis of type 1 diabetes can be made based on several criteria, including:
- Fasting plasma glucose level of 126 mg per dL or greater 2
- A1C level of 6.5% or greater 3, 2
- Random plasma glucose level of 200 mg per dL or greater 2
- 75-g two-hour oral glucose tolerance test with a plasma glucose level of 200 mg per dL or greater 3, 2
- Presence of anti-islet autoantibodies, such as antibodies to insulin, glutamic acid decarboxylase, tyrosine phosphatase-like protein IA-2, and zinc transporter 8 4, 5
Role of Autoantibodies in Diagnosis
Autoantibodies play a key role in the diagnosis of type 1 diabetes, particularly in distinguishing it from type 2 diabetes. The presence of multiple autoantibodies is thought to be more predictive of progression to overt diabetes than individual antibodies 4. A combinatorial analysis of anti-islet autoantibodies can help diagnose immune-mediated type 1 diabetes and slowly progressive type 1 diabetes (SPIDDM) or latent autoimmune diabetes in adults (LADA) 5.
Physical Examination and Screening
While screening for type 2 diabetes is recommended, screening for type 1 diabetes is not routinely recommended 2. The physical examination of a patient with diabetes can help confirm the diagnosis, classify the type of diabetes, and evaluate for macro- and microvascular complications and significant comorbid conditions 6. The U.S. Preventive Services Task Force recommends screening for abnormal blood glucose and type 2 diabetes in adults 40 to 70 years of age who are overweight or obese, and repeating testing every three years if results are normal 2.