What are the recommended times for measuring plasma glucose levels during an Oral Glucose Tolerance Test (OGTT) in non-pregnant patients, according to the American Diabetes Association (ADA) guidelines?

Timing of Plasma Glucose Measurements During OGTT in Non-Pregnant Patients

According to the American Diabetes Association (ADA) guidelines, the correct timing for measuring plasma glucose levels during an Oral Glucose Tolerance Test (OGTT) in non-pregnant patients is fasting and 2 hours (option D). 1

Standard OGTT Protocol for Non-Pregnant Adults

The ADA guidelines clearly specify the following protocol for OGTT in non-pregnant individuals:

• The test should be performed in the morning after an overnight fast of at least 8 hours
• A glucose load containing the equivalent of 75g anhydrous glucose dissolved in water is administered
• Plasma glucose measurements are taken at:
  • Fasting (before glucose load)
  • 2 hours after glucose load

Diagnostic Criteria for Diabetes in Non-Pregnant Adults

The diagnostic threshold for diabetes using the 2-hour OGTT value is:

• 2-hour plasma glucose ≥ 200 mg/dL (11.1 mmol/L) 1

Important Distinctions

It's crucial to understand that the timing of glucose measurements differs between:

1. Non-pregnant adults: Fasting and 2-hour measurements only
2. Pregnant women: Different protocols are used for gestational diabetes screening

Gestational Diabetes Testing (Different Protocol)

For pregnant women, the ADA recommends either:

• One-step strategy: 75g OGTT with measurements at fasting, 1-hour, and 2-hour 1
• Two-step strategy:
  • Step 1: 50g glucose load test (non-fasting) with measurement at 1-hour
  • Step 2: If positive, 100g OGTT with measurements at fasting, 1-hour, 2-hour, and 3-hour 1

Common Pitfalls to Avoid

• Don't confuse non-pregnant and gestational diabetes testing protocols: The question specifically asks about non-pregnant patients
• Don't assume additional measurement points are needed: While options B and C include more measurement points (which are used in research settings or for gestational diabetes), the standard clinical protocol for non-pregnant adults only requires fasting and 2-hour measurements
• Timing accuracy matters: Studies have shown that exact timing of samples is critical for accurate interpretation, as glucose values can change rapidly and unpredictably 2

The simplicity of the fasting and 2-hour protocol for non-pregnant adults makes it practical for clinical use while providing sufficient diagnostic information for diabetes classification.