Glucose Tolerance Test
Alternate Names : Oral Glucose Tolerance Test, OGTT, GTT
What do the test results mean?
Normal fasting blood glucose levels are less than
110 milligrams/deciliter, or mg/dL. If a person does not have diabetes, the
glucose levels will rise and then fall quickly after drinking the sweet liquid.
When a person has diabetes, glucose levels will rise higher and fail to come down
as fast as those in a person without diabetes. Healthy blood glucose levels after drinking
the glucose are less than 140 mg/dL. If the blood glucose level is 140 to 199 mg/dL
2 hours after drinking the liquid, a diagnosis of prediabetes can be made. If the
blood glucose level is higher than 200 mg/dL, then another test is done on a different day to confirm whether the person has
If levels are lower than normal, the person may have:
or low blood sugar
bowel problems that interfere with absorbing the glucose into the body
certain hormone imbalances, such as a
low thyroid hormone level
a tumor that causes the pancreas to make too much insulin, which is rare
certain substances in his or her body that interfere with the test, such as caffeine
If levels are higher than normal, the person may have:
hormone imbalances. These include a high thyroid hormone level or a high
level of cortisol, which is a hormone that is important in metabolism.
damage to the pancreas, which is the organ that secretes insulin. Insulin
is a hormone that helps keep the blood sugar from getting too high. When
damaged, the pancreas may not be able to secrete enough insulin.
certain tumors. For example, this may include tumors that
secrete adrenaline, a stress hormone.
certain medicines in his or her system that interfere with the test. This may
include corticosteroids or steroids.