- The oral glucose tolerance test (OGTT) is performed to rule out diabetes by evaluating the rate at which glucose is removed from the blood stream. Following administration of an oral glucose load, blood samples are drawn in 1/2, 1, 2, and 3 hours.
- For nondiabetic patients, the rise in blood glucose is relatively minor. For diabetic patients, however, the glucose level shows a dramatic increase and remains greatly elevated for several hours. This test is also used in screening for gestational diabetes during pregnancy.
- According to the American Diabetes Association, the corresponding categories when the OGTT is used are the following:
- 2-hour postload glucose <140 mg/dL = normal glucose tolerance;
- 2-hour postload glucose 140–199 mg/dL = impaired glucose tolerance (IGT);
- 2-hour postload glucose ≥200 mg/dL = provisional diagnosis of diabetes (the diagnosis must be confirmed).