The glucose tolerance test is a laboratory method to check how the body breaks down (metabolizes) sugar.
Alternative NamesOral glucose tolerance test
How the test is performedThe most common glucose tolerance test is the oral glucose tolerance test (OGTT). You cannot eat or drink anything after midnight before the test. For the test, you will be asked to drink a liquid containing a certain amount of glucose. Your blood will be taken before you do this, and again every 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. 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, although the timing may vary.
How to prepare for the testMake sure you eat normally for several days before the test.
Do not eat or drink anything for 8-10 hours before the test. You cannot eat during the test.
Ask your health care provider if you are using medications that can interfere with the test results.
How the test will feelSome people feel nauseated or sweaty after drinking the glucose for the test.
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 performedGlucose is the sugar the body uses for energy. Patients with untreated diabeteshave high blood glucose levels. Glucose tolerance tests are one of the tools used to diagnose Diabetes.
Above-normal blood 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 bloodstream 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 be used in cases where the disease is suspected, despite a normal fasting blood glucose level.
Normal ValuesNormal blood values for a 75-gram oral glucose tolerance test used to check for type 2 diabetes:
Normal blood values for a 50-gram oral glucose tolerance test used to screen for gestational diabetes:
Normal blood values for a 100-gram oral glucose tolerance test used to screen for gestational diabetes:
Note: mg/dL = milligrams per deciliter
Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
What abnormal results meanGreater than normal levels of glucose may mean you have diabetes or gestational diabetes.
However, high glucose levels may be related to another medical problem (for example, Cushing syndrome).
What the risks areVeins 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 more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
Factors that may affect the test results:
Several drugs may cause glucose intolerance, including:
Before having the test, let your health care provider know if you are taking any of these medications.
ReferencesAmerican Diabetes Association. Standards of medical care in diabetes -- 2010. Diabetes Care. 2010;33:S11-S61.
Inzucchi SE, Sherwin RS. Type 2 diabetes mellitus. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 248.
The standard test is a 3 hour GTT (glucose tolerance test).
A glucose test result of 129 mg/dL indicates that your blood sugar level is elevated. If this test was done without fasting, it may suggest impaired glucose tolerance or prediabetes, particularly if this is a random glucose test. Normal random glucose levels are typically below 140 mg/dL. It's advisable to discuss the results with a healthcare provider for further evaluation and possible follow-up testing.
To test for the amount of sugars (glucose) in the blood.
Just the presence of glucose Just the presence of glucose
Fasting is typically required for blood work that measures glucose levels, such as a fasting blood glucose test or an oral glucose tolerance test, as well as lipid panel tests that assess cholesterol and triglycerides. Fasting usually means no food or drink (except water) for 8-12 hours prior to the test. It's important to follow your healthcare provider's specific instructions regarding fasting for any blood work. Always consult with your doctor if you have questions about preparation for lab tests.
A common test to diagnose hypoglycemia is the extended oral glucose tolerance test.
The standard test is a 3 hour GTT (glucose tolerance test).
The glucose tolerance test is a lab test to check how your body breaks down sugar.
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A gray tube is typically used for a glucose tolerance test. This tube contains sodium fluoride as an additive to preserve glucose levels in the blood sample.
The tube used to test for glucose tolerance is typically a gray-top tube. This tube contains a preservative that helps prevent changes in glucose levels after the blood is drawn, ensuring accurate test results.
Chemistry
When I had a glucose tolerance test during pregnancy I was told to fast from midnight the night before, I was told to only drink water and nothing else, hope that helps!
No tubes are required. This can simply be done using a "fingerstick" glucose monitor.
It is generally recommended to fast for 8-12 hours before a glucose tolerance test, so it is best to avoid consuming anything, including water, during this fasting period. Water may dilute the glucose solution and affect the accuracy of the test results.
A GTT test stands for glucose tolerance test, which is used to measure how well the body processes sugar. During this test, gray-top tubes containing sodium fluoride and potassium oxalate are commonly used to collect blood samples for glucose measurements.