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Glucose tolerance test

The glucose tolerance test is a laboratory method tocheck how the body breaks down (metabolizes) sugar.
How the Test is Performed
The most common glucose tolerance test is the oral glucose tolerance test (OGTT). You cannot eat or drink anything for at least 8 hours before the test. For the test, you will be asked to drink a liquid containing a certain amount of glucose (usualy 75 grams). Your blood will be taken before you do this, and againevery 30 to 60 minutes after you drink the solution. The test takes up to 3 hours.
The intravenous glucose tolerance test (IGTT) is rarely used, and is never used to diagnose diabetes. In this test, glucose is injected into your vein for 3 minutes. Blood insulin levels are measured before the injection, and again at 1 and 3 minutes after the injection. However, the timing may vary.
How to Preparefor the Test
Make sure you eat normally for several days before the test.
Do not eat or drink anything for 8 hours before the test. You cannot eat during the test.
Ask your health care provider if any of the medicines you take can affect the test results.
How the Test Will Feel
Some people feel nauseated, sweaty, light-headed, or faint after drinking the glucose for the test. However, this isuncommon.
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the Test is Performed
Glucose is the sugar the body uses for energy. Patients with untreated diabetes have high blood glucose levels. Glucose tolerance tests are one of the tools used to diagnose diabetes.
Above-normalblood glucose levels can be used to diagnose type 2 diabetes or high blood glucose during pregnancy (gestational diabetes). Insulin levels may also be measured. (Insulin is the hormone produced by the pancreas that moves glucose from the blood into cells.)
The oral glucose tolerance test is used to screen pregnant women for gestational diabetes between 24 and 28 weeks of pregnancy. It may also beused when the disease is suspected, even though the fasting blood glucose level is normal.
Normal Results
Normal blood values for a 75-gram oral glucose tolerance test used to check for type 2 diabetes:
Fasting: 60 -100 mg/dL
1 hour: less than 200 mg/dL
2 hours: less than 140 mg/dL. Between 140 - 200 mg/dL is considered impaired glucose tolerance (sometimes called "prediabetes"). It meansyou are at increased risk for developing diabetes. A glucose level of 200 mg/dL or higher is a sign of diabetes.
Normal blood values for a 50-gram oral glucose tolerance test used to screen for gestational diabetes:
1 hour: equal to or less than 140 mg/dL
Normal blood values for a 100-gram oral glucose tolerance test used to screen for gestational diabetes:
Fasting: less than 95 mg/dL
1hour: less than 180 mg/dL
2 hour: less than 155 mg/dL
3 hour: less than 140 mg/dL
Note: mg/dL = milligrams per deciliter
The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.What Abnormal Results Mean
Higher-than-normal levels of glucose may mean you have prediabetes, diabetes, or gestational diabetes.
However, high glucose levels may be related to another medical problem (for example, Cushing syndrome).
Risks
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be...