What are normal Oral Glucose Tolerance Test (OGTT) results for non-pregnant individuals?

Normal OGTT Results for Non-Pregnant Individuals

For non-pregnant adults, a normal 2-hour plasma glucose during a 75-gram OGTT is less than 140 mg/dL (7.8 mmol/L). 1

Diagnostic Thresholds

The American Diabetes Association 2024 Standards of Care establish clear cutoffs that define the boundaries between normal, prediabetes, and diabetes for the OGTT 1:

Normal Range

• 2-hour plasma glucose: <140 mg/dL (<7.8 mmol/L) 1

Prediabetes (Impaired Glucose Tolerance)

• 2-hour plasma glucose: 140-199 mg/dL (7.8-11.0 mmol/L) 1

Diabetes

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

Critical Test Preparation Requirements

Patients must consume at least 150 grams of carbohydrates daily for the 3 days prior to the OGTT. 1 Fasting and carbohydrate restriction can falsely elevate glucose levels during the oral glucose challenge, leading to misdiagnosis 1.

The test requires an 8-hour fast before administration of 75 grams of anhydrous glucose dissolved in water, following WHO methodology 1.

Important Clinical Caveats

Sample Handling

Glycolysis is a critical and underrecognized concern that can falsely lower glucose concentrations if samples are not processed promptly or stored properly prior to analysis 1. This represents a common pitfall that can lead to false-negative results.

Factors Affecting Results

Several conditions can acutely affect glucose concentrations and should be considered when interpreting results 1:

• Recent physical activity 1
• Acute illness 1
• Acute stress 1
• High diurnal variation in glucose levels 1

Confirmatory Testing

In the absence of unequivocal hyperglycemia, diagnosis of diabetes requires two abnormal test results obtained either at the same time (e.g., A1C and fasting glucose) or at two different time points 1. This applies when the 2-hour value is ≥200 mg/dL.

Risk Continuum Concept

Risk is continuous across the entire glucose spectrum, extending below the lower limit of the prediabetes range and becoming disproportionately greater at the higher end. 1 This means that even values in the "normal" range carry some degree of risk, though substantially lower than prediabetes or diabetes ranges.

Alternative Diagnostic Tests

While the OGTT provides specific information about glucose handling, other tests can diagnose diabetes or prediabetes 1:

• Fasting plasma glucose (normal: <100 mg/dL) 1
• A1C (normal: <5.7%) 1

These tests reflect different aspects of glucose metabolism and will identify different groups of individuals 1.