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By Mayo Clinic staffThe glucose tolerance test is done in several steps. When you arrive at your doctor's office or lab, a member of your health care team will take a sample of blood by pricking your fingertip or inserting a needle into a vein in your arm. This blood sample will be used to measure your fasting blood glucose level.
Type 2 diabetes
If you're being tested for type 2 diabetes:
- You'll drink about 8 ounces (237 milliliters) of a syrupy glucose solution containing 2.6 ounces (75 grams) of sugar.
- Two hours later, your blood glucose level will be measured again.
Gestational diabetes
The American Congress of Obstetricians and Gynecologists recommends performing a one-hour blood glucose test first to screen for gestational diabetes in low-risk patients. If your doctor determines you're at risk or you have a suspicious value on the one-hour test, you may take the longer blood glucose test. For this test:
- You will be asked to come to the test fasting — not having had anything to eat or drink for the previous 8 hours. A fasting blood sugar will be obtained.
- You'll drink about 8 ounces (237 milliliters) of a glucose solution containing 3.5 ounces (100 grams) of sugar.
- Your blood glucose level will be tested again one, two and three hours after you drink the solution.
After drinking the glucose solution, you'll likely need to remain in the doctor's office or lab while you're waiting for your blood glucose level to be tested. After the glucose tolerance test, you can return to your usual activities immediately.
- American Diabetes Association. Standards of medical care in diabetes — 2013. Diabetes Care. 2013;36(suppl):1.
- Evensen AE. Update on gestational diabetes mellitus. Primary Care. 2012;39:83.
- Glucose. Lab Tests Online. http://labtestsonline.org/understanding/analytes/glucose/tab/glance. Accessed Dec. 7, 2012.
- McCullough DK. Diagnosis of diabetes mellitus. http://www.uptodate.com/index. Accessed Dec. 7, 2012.
- The American College of Obstetricians and Gynecologists (committee opinion). Screening and diagnosis of gestational diabetes mellitus. Obstetrics and Gynecology. 2011;118:751.
- Castro MR (expert opinion). Mayo Clinic, Rochester, Minn. April 8, 2013.
- Coustan DR, Jovanovic L. Screening and diagnosis of diabetes mellitus during pregnancy. http://www.uptodate.com/home. Accessed April 2, 2013.
- AskMayoExpert. What tests are needed to confirm the diagnosis of gestational diabetes mellitus during pregnancy? Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2013.
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