What are the diagnostic criteria and initial management for diabetes?

Diagnosis and Initial Management of Diabetes Mellitus

Diabetes mellitus is diagnosed when any of the following criteria are met: A1C ≥6.5%, fasting plasma glucose (FPG) ≥126 mg/dL, 2-hour plasma glucose ≥200 mg/dL during OGTT, or random plasma glucose ≥200 mg/dL with classic symptoms, requiring confirmation with a second test in the absence of unequivocal hyperglycemia. 1

Diagnostic Criteria for Diabetes

The American Diabetes Association (ADA) recommends diagnosing diabetes using any of these criteria:

1. A1C ≥6.5% (48 mmol/mol)

   • Must be performed using a method certified by the National Glycohemoglobin Standardization Program (NGSP)
   • Standardized to the Diabetes Control and Complications Trial (DCCT) reference assay

2. Fasting Plasma Glucose (FPG) ≥126 mg/dL (7.0 mmol/L)

   • Fasting defined as no caloric intake for at least 8 hours

3. 2-hour Plasma Glucose ≥200 mg/dL (11.1 mmol/L) during OGTT

   • Test performed using 75g anhydrous glucose dissolved in water

4. 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 (e.g., hyperglycemic crisis), diagnosis requires confirmatory testing 1
• Confirmation requires two abnormal results from the same test on different days or abnormal results from two different tests 2
• No repeat testing is required in symptomatic individuals with unequivocally elevated glucose >200 mg/dL 2

Classification of Diabetes

Diabetes is classified into several categories:

1. Type 1 Diabetes

   • Due to β-cell destruction, usually leading to absolute insulin deficiency
   • Often presents with classic symptoms and sometimes diabetic ketoacidosis (DKA)

2. Type 2 Diabetes

   • Due to progressive insulin secretory defect on the background of insulin resistance
   • Most common form, often associated with obesity and lifestyle factors

3. Gestational Diabetes Mellitus (GDM)

   • Diabetes diagnosed in the second or third trimester of pregnancy that is not clearly overt diabetes

4. Specific Types of Diabetes Due to Other Causes

   • Monogenic diabetes syndromes (e.g., neonatal diabetes, MODY)
   • Diseases of the exocrine pancreas (e.g., cystic fibrosis)
   • Drug or chemical-induced diabetes (e.g., with HIV/AIDS treatment or after organ transplantation) 1

Advantages and Limitations of Diagnostic Tests

A1C

• Advantages: No fasting required, greater preanalytical stability, less day-to-day variability during stress/illness 2
• Limitations: Higher cost, limited availability in some regions, incomplete correlation with average glucose in certain individuals 2

FPG

• Advantages: Wide availability, low cost 2
• Limitations: Requires 8-hour fasting, day-to-day variability of 12-15% 2

OGTT

• Advantages: Reference test, detects more cases than FPG 2
• Limitations: Poor reproducibility, requires 8-hour fasting and 2-hour stay, low patient adherence 2

Initial Management of Diabetes

1. Lifestyle Modifications

   • Healthy diet
   • Regular physical activity
   • Weight loss if overweight or obese 2

2. Pharmacotherapy

   • Metformin as initial pharmacotherapy unless contraindicated 2
   • Consider combination therapy if HbA1c ≥9% 2
   • Consider insulin (with or without other agents) if HbA1c ≥10% or glucose ≥300 mg/dL with symptoms 2
   • For type 1 diabetes, insulin therapy should be initiated immediately at diagnosis 2

Monitoring and Follow-up

• Regular monitoring of blood glucose levels
• Target HbA1c ≤7% for well-controlled diabetes 2, 3
• Screen for complications:
  • Microalbuminuria (early, reversible diabetic nephropathy)
  • Random urine albumin-creatinine ratio as screening test (0.03-0.30 g/g indicates microalbuminuria) 3
  • Regular eye examinations
  • Foot examinations

Common Pitfalls in Diagnosis

• Relying on a single test without confirmation in asymptomatic individuals
• Using point-of-care A1C testing for diagnosis (not recommended)
• Failing to consider conditions that affect A1C interpretation (hemoglobinopathies, anemia)
• Overlooking type 1 diabetes in adults (not exclusive to children)
• Overlooking type 2 diabetes in children (not exclusive to adults) 1

Tight glycemic control, which requires self-monitoring of blood glucose, reduces microvascular complications for patients with both type 1 and type 2 diabetes 3.