What are the initial diagnostic tests and treatment options for diabetes?

Diagnostic Tests and Treatment Options for Diabetes

The diagnosis of diabetes requires specific laboratory tests including fasting plasma glucose ≥126 mg/dL, 2-hour plasma glucose ≥200 mg/dL during oral glucose tolerance test, A1C ≥6.5%, or random plasma glucose ≥200 mg/dL with classic symptoms of hyperglycemia. 1

Diagnostic Criteria for Diabetes

Primary Diagnostic Tests

• A1C ≥6.5% (48 mmol/mol): Test should be performed using a method certified by the National Glycohemoglobin Standardization Program (NGSP) and standardized to the Diabetes Control and Complications Trial (DCCT) reference assay 1
• Fasting plasma glucose (FPG) ≥126 mg/dL (7.0 mmol/L): Fasting defined as no caloric intake for at least 8 hours 1
• 2-hour plasma glucose ≥200 mg/dL (11.1 mmol/L) during OGTT: Using 75g anhydrous glucose dissolved in water 1
• Random plasma glucose ≥200 mg/dL (11.1 mmol/L) in patients with classic symptoms of hyperglycemia (polyuria, polydipsia, unexplained weight loss) or hyperglycemic crisis 1

Confirmation Requirements

• In the absence of unequivocal hyperglycemia, diagnosis requires two abnormal test results:
  • Either from the same sample (e.g., A1C and FPG)
  • Or from two separate test samples 1
• If using two separate samples, the second test should be performed without delay 1
• When results from different tests are discordant, the test with results above the diagnostic threshold should be repeated 1

Special Considerations for A1C Testing

When to Avoid A1C Testing

A1C should not be used for diagnosis in conditions with altered relationship between A1C and glycemia:

• Hemoglobin variants
• Pregnancy (second and third trimesters)
• Postpartum period
• Glucose-6-phosphate dehydrogenase deficiency
• HIV infection
• Hemodialysis
• Recent blood loss or transfusion
• Erythropoietin therapy 1

In these cases, only plasma glucose criteria should be used for diagnosis 1.

Sample Handling

• Proper sample handling is critical as glycolysis can falsely lower glucose values
• Samples should be processed promptly or collected in tubes with glycolytic inhibitors 2
• For FPG and 2-h PG, samples must be spun and separated immediately after collection to prevent falsely low results 1

Prediabetes Diagnostic Criteria

Prediabetes is defined as:

• A1C 5.7-6.4% (39-47 mmol/mol), OR
• FPG 100-125 mg/dL (5.6-6.9 mmol/L) (impaired fasting glucose), OR
• 2-hour PG during 75-g OGTT 140-199 mg/dL (7.8-11.0 mmol/L) (impaired glucose tolerance) 1, 2

Initial Treatment Approaches

Type 1 Diabetes

• Insulin therapy is the cornerstone of treatment
• Multiple daily doses or continuous subcutaneous insulin infusion 2, 3
• Regular monitoring of blood glucose levels is essential 3

Type 2 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 initiating combination therapy if HbA1c ≥9% 2
   • Consider insulin (with or without other agents) if HbA1c ≥10% or glucose ≥300 mg/dL with symptoms 2

Common Pitfalls to Avoid

• Relying on a single test without confirmation in asymptomatic individuals 2
• Using point-of-care A1C tests for diagnosis (not sufficiently accurate) 1, 2
• Failing to consider conditions that affect A1C interpretation 2
• Improper sample handling leading to falsely low glucose values due to glycolysis 1, 2
• Not following proper OGTT protocol: Patients should consume a mixed diet with at least 150g of carbohydrates on the 3 days prior to OGTT 1

Screening Recommendations

• Testing should be considered in adults who are overweight or obese (BMI ≥25 kg/m² or ≥23 kg/m² in Asian Americans) with one or more risk factors 1
• Risk factors include first-degree relative with diabetes, high-risk race/ethnicity, history of cardiovascular disease, hypertension, HDL <35 mg/dL, triglycerides >250 mg/dL, polycystic ovary syndrome, physical inactivity, and other conditions associated with insulin resistance 1
• Testing should begin at age 45 years for those without risk factors 1
• If results are normal, testing should be repeated at minimum every 3 years 1

By following these diagnostic criteria and treatment approaches, clinicians can effectively identify and manage diabetes to reduce morbidity, mortality, and improve quality of life for patients.