Skip to content

    Diabetes Health Center

    Select An Article

    What Is the Oral Glucose Tolerance Test?

    Font Size
    A
    A
    A

    Although doctors don't routinely use it anymore, the oral glucose tolerance test is the gold standard for diagnosing type 2 diabetes. It's still commonly used to diagnose gestational diabetes, a condition that a woman can get while pregnant.

    You’ll fast for at least 8 hours -- but not more than 16 -- the night before you take the test. When you get to the doctor’s office, he’ll test your fastingblood sugar. Afterward, you’ll get 75 grams of glucose (100 grams for pregnant women), usually in the form of a sweet-tasting liquid that you drink. The doctor will take blood samples up to four times to measure your blood sugar levels.

    Recommended Related to Diabetes

    Diabetes-Friendly Summer Grill Recipes

    Kathleen Zelman, MPH, RD, LD, WebMD's director of nutrition, created this delicious and colorful meal of grilled salmon with black bean corn salsa and salad. It's a low-calorie lunch or dinner that is rich in fiber, antioxidants, and heart-healthy omega-3 fatty acids. The balance of complex carbs, protein, and good fats makes it diabetes-friendly, too. Southwestern Grilled Salmon Makes 4 servings Ingredients cooking spray 1 tsp ground cumin 1 tsp chili powder dash of salt freshly...

    Read the Diabetes-Friendly Summer Grill Recipes article > >

    Obstetricians use several methods to do this test, but the one described here is standard.

    How Reliable Is the Test?

    For the oral glucose tolerance test to give reliable results, you have to be in good health. You can’t have any other illnesses -- not even a cold. And you can’t be taking drugs that could affect your blood sugar.

    You'll have to watch your carbs beforehand, too. Don’t eat more than 150 to 200 grams a day for 3 days before the test. Don’t smoke or drink coffee the morning of the test, either.

    What Does It Measure?

    The classic oral glucose tolerance test measures blood sugar levels over a period of 3 hours. Some doctors simply get a beginning blood sample, followed by a sample 2 hours after you drink the glucose solution.

    If you don’t have diabetes, your blood sugar levels will rise and then fall quickly. If you do have it, the levels rise higher than normal and don’t come back down as fast.

    If the test shows that your levels are between normal and diabetic, you have what doctors call impaired glucose tolerance (IGT). People with IGT don’t have diabetes yet.

    If you have a high blood sugar level, weight loss and exercise may help return it to normal. Some doctors suggest medications like metformin (Glucophage) to help prevent or delay the onset of diabetes.

    WebMD Medical Reference from MedicineNet

    Reviewed by Michael Dansinger, MD on February 01, 2016
    Next Article:

    Today on WebMD

    Diabetic tools
    Symptoms, diagnosis, treatment, and more.
    woman flexing muscles
    10 strength training exercises.
     
    Blood sugar test
    12 practical tips.
    Tom Hanks
    Stars living with type 1 or type 2.
     
    kenneth fujioka, md
    Video
    Can Vinegar Treat Diabetes
    Article
     
    Middle aged person
    Tool
    jennie brand miller
    Video
     

    Prediabetes How to Prevent Type 2 Diabetes
    Article
    type 2 diabetes
    Slideshow
     
    food fitness planner
    Tool
    feet
    Slideshow