A glucose tolerance test in medical practice is the administration of glucose to determine how quickly it is cleared from the blood. The test is usually used to test for diabetes, insulin resistance, and sometimes reactive hypoglycemia. The glucose is most often given orally so the common test is technically an oral glucose tolerance test (OGTT). The test may be performed as part of a panel of tests, such as the comprehensive metabolic panel.

How the Test is Performed?  

Glucose is the sugar that 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.The most common glucose tolerance test is the oral glucose tolerance test (OGTT). You can not 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.

Blood glucose levels above normal limits at the times measured can be used to diagnose type 2 diabetes or gestational diabetes (high blood glucose during pregnancy). Insulin levels may also be measured. (Insulin is the hormone produced by the pancreas that moves glucose from the bloodstream into cells).The intravenous glucose tolerance test (IGTT) is not often 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. This test may predict the development of type 1 diabetes in some patients.

How is the screening test done?

When you arrive for the test, you’ll be given a sugar solution that contains 50 grams of glucose. The stuff tastes like a very sweet soda pop (it comes in cola, orange, or lime flavor), and you have to get all of it down in five minutes. Some centers keep it chilled or let you pour it over ice and drink it cold.

Glucose tolerance diagnostic test

To prepare for the glucose tolerance diagnostic test: Eat a balanced diet that contains 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. Tell your health professional about all prescription and nonprescription medicines you are taking. You may be instructed to stop taking certain medicines before the test. The glucose tolerance diagnostic test may take up to 4 hours. Since activity can interfere with test results, you will be asked to sit quietly during the entire test. Do not eat during the test. You may drink only water during this time.

What if my Glucose Tolerance Test Results are Abnormal?

If only one of your readings comes back abnormal, your doctor may suggest some changes to your diet and/or test you again later in the pregnancy. If two or more of your readings come back abnormal, you’ll be diagnosed with Gestational Diabetes and your doctor or midwife will talk to you about a treatment plan. Treating diabetes during pregnancy is extremely important to protect the health of both mother and baby

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