What are the diagnostic criteria and treatment options for confirming type one diabetes?

Diagnostic Criteria and Treatment Options for Type 1 Diabetes

The primary diagnostic approach for type 1 diabetes involves measuring plasma glucose in symptomatic patients (≥200 mg/dL with classic symptoms) and testing for islet autoantibodies, starting with glutamic acid decarboxylase (GAD) antibodies, followed by additional antibodies if needed. 1

Diagnostic Criteria

Primary Diagnostic Tests

• In patients with classic symptoms (polyuria, polydipsia, weight loss, fatigue), a random plasma glucose ≥200 mg/dL (11.1 mmol/L) is sufficient to diagnose diabetes 2
• For patients without classic symptoms, diagnosis requires two abnormal test results from the same sample or in two separate test samples 2
• Acceptable diagnostic tests include:
  • Fasting plasma glucose (FPG) ≥126 mg/dL (7.0 mmol/L) after at least 8 hours of fasting 2
  • 2-hour plasma glucose ≥200 mg/dL (11.1 mmol/L) during an oral glucose tolerance test (OGTT) 2
  • A1C ≥6.5% (48 mmol/mol) using a method that is NGSP certified and standardized to the DCCT assay 2

Confirming Type 1 Diabetes

• Islet autoantibody testing is recommended to confirm type 1 diabetes, particularly in adults with phenotypic features that overlap with type 2 diabetes 1
• The primary antibodies to test for include:
  • Glutamic acid decarboxylase (GAD) antibodies (first-line test) 1, 3
  • Islet tyrosine phosphatase 2 (IA-2) antibodies 1, 3
  • Zinc transporter 8 (ZnT8) antibodies 1, 3
  • Insulin autoantibodies (IAA) - particularly useful in patients not yet treated with insulin 1, 4
• The presence of multiple autoantibodies indicates a higher risk of progression to insulin dependence 1, 5
• C-peptide testing can assess residual β-cell function but should not be performed within 2 weeks of a hyperglycemic emergency 1

Staging of Type 1 Diabetes

Type 1 diabetes develops in three distinct stages:

1. Stage 1: Presence of two or more islet autoantibodies with normoglycemia (presymptomatic) 2, 5
2. Stage 2: Presence of islet autoantibodies with dysglycemia (presymptomatic) 2, 5
3. Stage 3: Clinical diabetes with overt hyperglycemia (symptomatic) - this is when most patients are diagnosed 2, 1

Treatment Options

Insulin Therapy

• Insulin replacement therapy is essential and lifelong for patients with type 1 diabetes 6, 3
• Common insulin regimens include:
  • Basal-bolus regimen with long-acting insulin (e.g., insulin glargine) once daily at bedtime and rapid-acting insulin before meals 6
  • Multiple daily injections (MDI) with combinations of rapid-acting and long-acting insulins 6
  • Continuous subcutaneous insulin infusion (insulin pump therapy) 7

Monitoring and Management

• Regular blood glucose monitoring is essential, with continuous glucose monitoring (CGM) systems providing more comprehensive data 7
• Automated insulin delivery systems (hybrid closed-loop systems) can improve glycemic control and reduce hypoglycemia 7
• Regular screening for complications is necessary, including retinopathy, nephropathy, neuropathy, and cardiovascular disease 8

Special Considerations and Pitfalls

• A1C should not be used as the sole diagnostic test in conditions with altered red blood cell turnover (pregnancy, hemoglobinopathies, recent blood loss, hemodialysis) 2
• Point-of-care A1C assays should not be used for diagnosis unless FDA-cleared specifically for diagnostic purposes 1
• Approximately 5-10% of adult-onset type 1 diabetes may be autoantibody negative, requiring clinical judgment for diagnosis 1
• Samples for plasma glucose should be spun and separated immediately after collection to prevent falsely low results 2
• Patients should consume a mixed diet with at least 150g of carbohydrate on the 3 days prior to oral glucose tolerance testing 2

Screening for Type 1 Diabetes Risk

• Screening for type 1 diabetes risk with islet autoantibodies is currently recommended only in research settings or for first-degree relatives of individuals with type 1 diabetes 2
• The presence of two or more autoantibodies is highly predictive of progression to clinical type 1 diabetes 2, 5