What are the normal values for glucose tolerance?

When evaluating patients suspected of having diabetes, physicians typically perform an oral glucose tolerance test (OGTT). Glucose tolerance refers to the body’s ability to metabolize and regulate glucose. The OGTT is especially recommended for screening gestational diabetes. So, what are the normal reference values for this test?

What Are the Normal Values for the Oral Glucose Tolerance Test?

Normal glucose tolerance values are as follows: fasting blood glucose ranges from 3.9–6.1 mmol/L, and 2-hour postprandial (or 2-hour post-glucose load) blood glucose should not exceed 7.8 mmol/L. If either fasting or 2-hour postprandial blood glucose falls outside these normal ranges, an OGTT is indicated to confirm or rule out diabetes. A diagnosis of diabetes can be established if the fasting blood glucose level is ≥7.0 mmol/L or the 2-hour post-glucose-load blood glucose level is ≥11.1 mmol/L—provided these abnormal results are confirmed on two separate occasions.

Fasting blood glucose between 6.1 mmol/L and 7.0 mmol/L (i.e., above the upper limit of normal but below the diabetic threshold) is termed “impaired fasting glucose.” Similarly, a 2-hour post-glucose-load blood glucose level between 7.8 mmol/L and 11.1 mmol/L (i.e., above normal but below the diagnostic threshold for diabetes) is termed “impaired glucose tolerance.”

Both impaired fasting glucose and impaired glucose tolerance fall under the category of “prediabetes”—a condition characterized by blood glucose levels higher than normal but not yet meeting the diagnostic criteria for diabetes. We hope this information has been helpful!