What are the diagnostic criteria for Diabetes Mellitus (DM) type 2?

Diagnostic Criteria for Type 2 Diabetes Mellitus

Type 2 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), HbA1c ≥6.5%, or a random plasma glucose ≥200 mg/dL (11.1 mmol/L) with symptoms of hyperglycemia. 1

Diagnostic Tests and Criteria

Primary Diagnostic Criteria

• Fasting Plasma Glucose (FPG)

  • ≥126 mg/dL (7.0 mmol/L)
  • Fasting defined as no caloric intake for at least 8 hours

• 2-hour Plasma Glucose (2hPG) during OGTT

  • ≥200 mg/dL (11.1 mmol/L)
  • Test performed using 75g anhydrous glucose dissolved in water

• Hemoglobin A1C (HbA1c)

  • ≥6.5% (48 mmol/mol)
  • Test must be performed using a method that is NGSP-certified and standardized to the DCCT assay

• Random Plasma Glucose

  • ≥200 mg/dL (11.1 mmol/L)
  • Must be accompanied by classic symptoms of hyperglycemia (polydipsia, polyuria, polyphagia, and weight loss) 1

Confirmation Requirements

• In the absence of unequivocal hyperglycemia, results should be confirmed by repeat testing 1
• Individuals with no typical symptoms of diabetes must be retested to confirm the diagnosis 1

Prediabetes Criteria

Prediabetes is diagnosed when test results fall within these ranges:

• Impaired Fasting Glucose (IFG)

  • FPG 100-125 mg/dL (5.6-6.9 mmol/L) 1

• Impaired Glucose Tolerance (IGT)

  • 2-hour PG during OGTT 140-199 mg/dL (7.8-11.0 mmol/L) 1

• HbA1c

  • 5.7-6.4% (39-47 mmol/mol) 1

Diagnostic Algorithm

1. Initial Screening:

   • For asymptomatic individuals with risk factors (BMI ≥25 kg/m² or ≥23 kg/m² in Asian Americans, family history, high-risk ethnicity, hypertension, etc.)
   • Begin with either FPG, HbA1c, or OGTT 1

2. Symptomatic Patients:

   • If classic symptoms present (polydipsia, polyuria, polyphagia, weight loss), perform random plasma glucose
   • If ≥200 mg/dL (11.1 mmol/L), diagnosis is confirmed 1

3. Asymptomatic Patients:

   • If initial test is abnormal, confirm with a second test
   • If two different tests (e.g., FPG and HbA1c) are both above diagnostic thresholds, diagnosis is confirmed
   • If results are discordant, repeat the test with the higher result 1

Special Considerations

HbA1c Limitations

• Not recommended as the sole diagnostic test in certain populations:
  • Pregnancy
  • Hemoglobinopathies
  • Conditions with abnormal red cell turnover (hemolytic anemia, iron deficiency)
  • Certain ethnic groups where correlation with glucose may differ 1

Testing in Children and Adolescents

• Consider testing in overweight (≥85th percentile) or obese (≥95th percentile) children with additional risk factors:
  • Family history of type 2 diabetes
  • High-risk race/ethnicity
  • Signs of insulin resistance
  • Maternal history of diabetes or GDM 1

Gestational Diabetes Screening

• Not part of type 2 diabetes diagnosis but important for comprehensive diabetes care
• Screening recommended at 24-28 weeks of gestation in pregnant women not previously diagnosed with diabetes 1

Common Pitfalls to Avoid

1. Pre-analytical Errors:

   • Failure to ensure proper fasting status before FPG testing
   • Delayed processing of samples leading to falsely low glucose values due to glycolysis

2. Analytical Errors:

   • Using point-of-care HbA1c testing that is not NGSP-certified
   • Improper OGTT technique (incorrect glucose load, timing)

3. Interpretation Errors:

   • Diagnosing diabetes based on a single abnormal test in asymptomatic individuals
   • Failing to consider conditions that may affect HbA1c results

4. Follow-up Errors:

   • Not retesting individuals with prediabetes at appropriate intervals (yearly for prediabetes, every 3 years for normal results) 1

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