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You are here : 3-RX.com > Medical Encyclopedia > Tests and Exams > Glucose Tolerance Test: Results and Values
      Category : Health Centers > Diabetes

Glucose Tolerance Test

Alternate Names : Oral Glucose Tolerance Test, OGTT, GTT

Glucose Tolerance Test | Preparation & Expectations | Results and Values

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 diabetes.

If levels are lower than normal, the person may have:

  • hypoglycemia, 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:

  • prediabetes
  • diabetes mellitus
  • gestational diabetes
  • 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.

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    Glucose Tolerance Test: Preparation & Expectations


    Author: David T. Moran, MD
    Reviewer: Kathleen A. MacNaughton, RN, BSN
    Date Reviewed: 06/24/02

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