Glucose Tolerance Test
Medical Author: Ruchi Mathur, MD
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR
What is the glucose tolerance test?
Though not routinely used anymore,
the oral glucose tolerance test (OGTT) is the gold standard for making the
diagnosis of type 2 diabetes. It is still commonly used for diagnosing
gestational diabetes. With an oral glucose tolerance test, the person fasts
overnight (at least 8 but not more than 16 hours). Then first, the fasting
plasma glucose is tested. After this test, the person receives 75 grams of
glucose (100 grams for pregnant women). There are several methods
employed by obstetricians to do this test, but the one described here is
standard. Usually, the glucose is in a sweet-tasting liquid that the person
drinks. Blood samples are taken up to four times to measure the blood glucose.
How reliable is the glucose tolerance test?
For the glucose tolerance test to give reliable results, the person must
be in good health (not have any other illnesses, not even a
cold). Also, the person should be normally
active (not lying down, for example, as an inpatient in a hospital) and should
not be taking medicines that could affect the blood glucose. For three days before
the test, the person should have eaten a diet high in carbohydrates (150- 200
grams per day). The morning of the test, the person should not
smoke or drink
coffee.
Next: What does the glucose tolerance test measure? »
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