Glucose Tolerance TestThe oral glucose tolerance test (OGTT) is a blood test which measures the ability of the body to use a type of sugar called glucose, which is the major source of energy for the body. This test can be used to diagnose prediabetes and diabetes and is used most commonly in pregnant patients to test for gestational diabetes. There are three versions of the oral glucose tolerance test. After reading this page you will be familiar with the uses for the different tests, you will be aware of any required pre-testing preparation and what to expect if you have to be tested. One hour glucose tolerance test (1-hr GTT) is a screening test for gestational diabetes, it is a routine test for all pregnant women (except those with known diabetes) and is usually done during the 24th to the 28th week of pregnancy. No special preparation is needed for the 1-hr GTT. You can eat normally and drink normally on the day of testing. You will be asked to drink a very sweet liquid containing 50 grams of glucose. It is best to drink the liquid quickly. A blood sample will be collected 1 hour after you drink the glucose. In most cases you will get your results at your next antenatal visit. However, if the results are abnormal you will probably be notified sooner so that counseling and management can begin. The two-hour glucose tolerance test is for postpartum patients who were diagnosed with gestational diabetes. Done not less than six weeks after delivery, its purpose is to determine which patients with gestational diabetes require further management for outright diabetes and which were indeed only experiencing a pregnancy-related condition. It is not possible to differentiate these without such testing. The three-hour glucose tolerance test (3-hr GTT) is used in pregnancy to confirm the presence of diabetes in patients who tested positive on the screening 1-hr OGTT. Unlike the 1-hr test, the 3-hr GTT requires the following preparation and precautions: * Eat a balanced diet with at least 150 to 200 grams (g) of carbohydrate per day for 3 days before the test. Fruits, breads, cereals, grains, rice, crackers, and starchy vegetables such as potatoes, beans, and corn are good sources of carbohydrate. * Do not eat, drink, smoke, or exercise strenuously for at least 8 hours before your first blood sample is taken. Do not eat anything nor exercise during the test. * Tell your doctor about all prescription and nonprescription medicines you are taking. You may be instructed to stop taking certain medicines before the test since they can affect your results.
* Diagnose prediabetes and diabetes. How the oral glucose tolerance test will feel
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