What are the diagnostic criteria for diabetes type 2 (diabetes mellitus type 2)?

Diagnostic Criteria for Type 2 Diabetes Mellitus

Type 2 diabetes is diagnosed when any one of the following criteria is met: fasting plasma glucose ≥126 mg/dL (7.0 mmol/L), 2-hour plasma glucose ≥200 mg/dL (11.1 mmol/L) during an oral glucose tolerance test, A1C ≥6.5% (48 mmol/mol), or random plasma glucose ≥200 mg/dL (11.1 mmol/L) with classic symptoms of hyperglycemia. 1

Primary Diagnostic Criteria

• Fasting Plasma Glucose (FPG): ≥126 mg/dL (7.0 mmol/L), with fasting defined as no caloric intake for at least 8 hours 1
• 2-hour Plasma Glucose (2-h PG): ≥200 mg/dL (11.1 mmol/L) during a 75-g oral glucose tolerance test (OGTT) performed as described by the World Health Organization 1
• Hemoglobin 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
• 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

Confirmation Requirements

• In the absence of unequivocal hyperglycemia with acute metabolic decompensation, diagnosis requires two abnormal test results from the same sample or in two separate test samples 1
• If using two different tests (such as A1C and FPG) and both are above diagnostic thresholds, the diagnosis is confirmed 1
• If results are discordant from two different tests, the test with results above the diagnostic threshold should be repeated 1
• When a patient has classic symptoms of hyperglycemia or hyperglycemic crisis with a random plasma glucose ≥200 mg/dL (11.1 mmol/L), no confirmation is needed 1

Prediabetes Criteria

• Fasting Plasma Glucose: 100-125 mg/dL (5.6-6.9 mmol/L) - Impaired Fasting Glucose (IFG) 1
• 2-hour Plasma Glucose: 140-199 mg/dL (7.8-11.0 mmol/L) during OGTT - Impaired Glucose Tolerance (IGT) 1
• A1C: 5.7-6.4% (39-47 mmol/mol) 1

Special Considerations for A1C Testing

• A1C should not be used for diagnosis in conditions affecting red blood cell turnover, including:
  • Hemoglobinopathies and hemolytic anemias 2
  • Pregnancy (second and third trimesters) 2
  • Recent blood loss or transfusion 2
  • Hemodialysis 2
  • Erythropoietin therapy 2
• In these conditions, only plasma glucose criteria should be used 1
• Marked discordance between measured A1C and plasma glucose levels should raise the possibility of hemoglobin variants interfering with the assay 1

Point-of-Care A1C Testing

• Point-of-care A1C assays may be used in CLIA-certified settings that meet quality standards 1
• These standards include:
  • Personnel requirements with documented annual competency assessments 1
  • Participation three times per year in approved proficiency testing programs 1
• While convenient for monitoring glycemic control, caution is advised when using point-of-care A1C testing for diagnosis 1

Limitations of Different Testing Methods

• FPG: Requires 8-hour fast and has high diurnal variation 2
• OGTT: Low reproducibility, requires 8-hour fast and 75g glucose load 2
• A1C: May be affected by conditions impacting red blood cell turnover; not universally available in all regions globally 2

Clinical Pearls

• Type 2 diabetes accounts for 90-95% of all diabetes cases 1
• The diagnosis of diabetes should be made as early as possible to prevent complications related to chronic hyperglycemia 1
• Even undiagnosed patients are at increased risk of developing macrovascular and microvascular complications 1
• For optimal OGTT results, patients should consume a mixed diet with at least 150g of carbohydrates in the 3 days preceding the test 2
• The concordance between FPG, 2-h PG, and A1C tests is imperfect; they do not necessarily detect diabetes in the same individuals 1

By following these diagnostic criteria, clinicians can accurately identify patients with type 2 diabetes and initiate appropriate management to reduce the risk of complications and improve outcomes.