What are the diagnostic criteria and initial treatment for diabetes?

Diagnostic Criteria and Initial Treatment for Diabetes

Diabetes is diagnosed when any of the following criteria are met: fasting plasma glucose (FPG) ≥126 mg/dL (7.0 mmol/L), 2-hour plasma glucose ≥200 mg/dL (11.1 mmol/L) during an oral glucose tolerance test (OGTT), hemoglobin A1C ≥6.5%, or random plasma glucose ≥200 mg/dL (11.1 mmol/L) with classic symptoms of hyperglycemia. 1, 2

Diagnostic Criteria

Primary Diagnostic Tests

• FPG ≥126 mg/dL (7.0 mmol/L), with fasting defined as no caloric intake for at least 8 hours 1, 2
• 2-hour plasma glucose ≥200 mg/dL (11.1 mmol/L) during a 75-g OGTT performed according to World Health Organization standards 1, 3
• A1C ≥6.5% (48 mmol/mol), performed in a laboratory using a method certified by the National Glycohemoglobin Standardization Program (NGSP) and standardized to the Diabetes Control and Complications Trial (DCCT) assay 1, 2
• Random plasma glucose ≥200 mg/dL (11.1 mmol/L) in a patient with classic symptoms of hyperglycemia (polyuria, polydipsia, unexplained weight loss) or hyperglycemic crisis 1, 2

Confirmation Requirements

• In the absence of unequivocal hyperglycemia with acute metabolic decompensation, diagnosis requires confirmation with repeat testing 1
• Confirmation can be done by:
  • Repeating the same test on a different day 1
  • Using a different test (e.g., if FPG is the initial test, A1C can be the confirmatory test) 1
  • Measuring two different tests (glucose and A1C) in samples obtained on the same day 1
• No confirmation is needed for symptomatic individuals with unequivocal hyperglycemia >200 mg/dL (11.1 mmol/L) 1

Prediabetes Criteria

• FPG: 100-125 mg/dL (5.6-6.9 mmol/L) - Impaired Fasting Glucose (IFG) 2, 3
• 2-hour plasma glucose: 140-199 mg/dL (7.8-11.0 mmol/L) - Impaired Glucose Tolerance (IGT) 2, 3
• A1C: 5.7-6.4% (39-47 mmol/mol) 2, 3

Special Considerations

A1C Testing Limitations

• A1C should not be used for diagnosis in conditions affecting red blood cell turnover, including: 1, 3
  • Hemoglobinopathies
  • Hemolytic anemias
  • Pregnancy (second and third trimesters)
  • Glucose-6-phosphate dehydrogenase deficiency
  • Recent blood loss or transfusion
  • Hemodialysis
  • Erythropoietin therapy
• In these conditions, only plasma glucose criteria should be used for diagnosis 1, 3

OGTT Considerations

• Patients should consume a mixed diet with at least 150g of carbohydrates on the 3 days preceding the test 1
• Fasting and carbohydrate restriction can falsely elevate glucose levels during an oral glucose challenge 1

Classification of Diabetes

Type 1 Diabetes

• Accounts for 5-10% of diabetes cases 1
• Characterized by autoimmune destruction of pancreatic β-cells 1
• Autoimmune markers include islet cell autoantibodies and autoantibodies to glutamic acid decarboxylase (GAD), insulin, tyrosine phosphatases, and zinc transporter 8 1

Type 2 Diabetes

• Accounts for 90-95% of all diabetes cases 2
• Characterized by insulin resistance and relative insulin deficiency 4
• Body does not make enough insulin, and the insulin produced does not work effectively 4

Initial Treatment Approach

Lifestyle Modifications

• Diet and exercise are the first-line interventions for lowering blood sugar 4
• Weight reduction can improve insulin resistance but seldom restores it to normal 2

Pharmacological Treatment

• Metformin is typically the first-line medication for type 2 diabetes 4
• Metformin works by decreasing glucose production in the liver and improving insulin sensitivity 4
• Side effects may include gastrointestinal symptoms and a metallic taste (in about 3% of patients) 4

Monitoring

• Self-monitoring of blood glucose is integral to effective therapy 1
• HbA1c testing should be performed at least twice yearly in patients meeting treatment goals with stable glycemic control 1
• Quarterly HbA1c testing is recommended for patients whose therapy has changed or who are not meeting glycemic goals 1

Clinical Pearls and Pitfalls

• The concordance between FPG, 2-h PG, and A1C tests is imperfect; they do not necessarily detect diabetes in the same individuals 2
• Marked discrepancy between measured A1C and plasma glucose levels should raise the possibility of hemoglobin variants interfering with the assay 3
• Misdiagnosis of diabetes type can occur in up to 40% of adults with new type 1 diabetes who are misdiagnosed as having type 2 diabetes 2
• Early diagnosis is critical as even undiagnosed patients are at increased risk of developing macrovascular and microvascular complications 2, 3