The glucose tolerance test, also known as the oral glucose tolerance test, measures your body's response to sugar (glucose). The glucose tolerance test can be used to screen for type 2 diabetes. More commonly, a modified version of the glucose tolerance test is used to diagnose gestational diabetes — a type of diabetes that develops only during pregnancy. The glucose tolerance test identifies abnormalities in the way your body handles glucose after a meal — often before your fasting blood glucose level becomes abnormal. 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). 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.