What is an Oral Glucose Tolerance Test?

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  • Written By: J.M. Willhite
  • Edited By: Heather Bailey
  • Last Modified Date: 10 August 2019
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An oral glucose tolerance test (OGTT) is a diagnostic tool used to evaluate how an individual’s body metabolizes sugar. Often used to diagnose diabetic conditions, an oral glucose tolerance test requires minimal preparatory measures and may be safely administered during pregnancy. An OGTT does carry minimal risk for complications and these should be discussed with a qualified health care professional prior to test administration.

Under normal circumstances, the body utilizes the sugar consumed through one’s diet as fuel. When the body fails to metabolize consumed sugar, it accumulates, triggering an imbalance that can result in a pre-diabetic condition that places the body at risk for complications that may impair its ability to function properly. The presence of consistently high blood glucose levels is generally indicative of pre-diabetes, which is considered to be a precursor to the development of type 2 diabetes. It has been estimated that nearly 57 million people in the United States alone have pre-diabetes which may be detected through the administration of an oral glucose tolerance test.


Similarly, when a woman becomes pregnant, she may possess an elevated risk for developing gestational diabetes. The presence of this form of diabetes is often temporary and subsides once a woman has given birth. During the interim, it is important for her to monitor her blood glucose levels to lessen the risk for complications for both her and her unborn child. As a precautionary measure, it is not uncommon for an oral glucose tolerance test to be utilized as a screening tool to detect this diabetic condition.

There are minimal preparatory measures required for an oral glucose tolerance test. Individuals are generally instructed to maintain their normal diet in the weeks and days leading up to the test so that test results may possess an accurate foundation. Though fasting for a minimum of four hours is required prior to test administration to prevent a false reading, an individual is usually instructed to not consume any food or beverage for at least 12 hours prior to testing.

The test carries minimal risk for complications that may include excessive bleeding, light-headedness, and hematoma formation at the injection site. Certain prescription drugs may interfere with the metabolic processes associated with this type of test, including beta-blockers and oral contraceptive medications. Individuals should consult with their health care provider regarding potential drug interactions prior to test administration.

The oral glucose tolerance test is multifaceted in its administration and may take several hours to complete. Following the initial fast, a blood draw will be performed with the aid of a small needle. Obtained from a vein, the blood draw is generally a relatively painless procedure. Some individuals may experience slight, momentary discomfort as the needle is inserted and a dull ache when the needle is withdrawn.

After the blood draw, the individual is given a liquid glucose solution to drink, which may induce nausea. Subsequent blood samples may then be periodically taken for up to three hours following the administration of the sugary solution. Each blood sample taken serves as a snapshot of the metabolizing process as the body processes the sugar consumed. The overall picture created by the multiple blood draws may then be interpreted to evaluate the resulting blood sugar levels. At the conclusion of the test, high blood glucose levels are generally indicative of the presence of diabetes.


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