What is the glucose tolerance test?
Though no longer routinely used for diagnosing diabetes. The oral glucose tolerance test (OGTT) was the gold standard for making the diagnosis of type 2 diabetes. It is still commonly used during pregnancy for diagnosing gestational diabetes. With an oral glucose tolerance test, the person fasts overnight (at least 8 hours, but not more than 16 hours). The next morning, the fasting plasma glucose is tested. After this test, the person receives a dose of oral glucose (the dose depends upon the length of the test). There are several methods employed by obstetricians to do this test, but the one described here is standard. Usually, the glucose is in a sweet-tasting liquid that the person drinks. Blood samples are taken up to four times at different time points after consumption of the sugar to measure the blood glucose.
How reliable is the glucose tolerance test?
For the glucose tolerance test to give reliable results, the person must be in good health (not have any other illnesses, not even a common cold). Also, the person should be normally active (not lying down, for example, as an inpatient in a hospital) and should not be taking medicines that could affect the blood glucose. In preparation for the oral glucose tolerance test, the person should eat and drink as they normally would. The morning of the test, the person should not smoke or consume caffeine.