How does the oral glucose tolerance test define diabetes and prediabetes?

Emilia Klapp
Nutrition & Dietetics Specialist

This is another test to diagnose diabetes and also can indicate insulin resistance. It is a blood test done two hours after a person ingests 75 g of glucose dissolved in water.

A result of more than 200 mg/dL (milligrams per deciliter) is a provisional diagnosis of diabetes. The diagnosis must be confirmed with a second test. A normal test result is less than 140 mg/dL. A result of more than 140 but less than 199 mg/dL indicates prediabetes.

In the oral glucose tolerance test (OGTT), a person's blood glucose is measured after a fast and 2 hours after drinking a glucose-rich beverage. Normal blood glucose is below 140 mg/dl 2 hours after the drink. In prediabetes, the 2-hour blood glucose is 140 to 199 mg/dl. If the 2-hour blood glucose rises to 200 mg/dl or above, a person has diabetes.

Continue Learning about Diabetes


Diabetes mellitus (MEL-ih-tus), often referred to as diabetes, is characterized by high blood glucose (sugar) levels that result from the body’s inability to produce enough insulin and/or effectively utilize the insulin. Diabetes ...

is a serious, life-long condition and the sixth leading cause of death in the United States. Diabetes is a disorder of metabolism (the body's way of digesting food and converting it into energy). There are three forms of diabetes. Type 1 diabetes is an autoimmune disease that accounts for five- to 10-percent of all diagnosed cases of diabetes. Type 2 diabetes may account for 90- to 95-percent of all diagnosed cases. The third type of diabetes occurs in pregnancy and is referred to as gestational diabetes. Left untreated, gestational diabetes can cause health issues for pregnant women and their babies. People with diabetes can take preventive steps to control this disease and decrease the risk of further complications.

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