The glucose tolerance test is a method to judge how well your body is able to metabolize glucose. Glucose is the type of sugar your body uses to supply energy to its cells. Your body breaks down the food you eat into glucose that then enters your bloodstream. A hormone called insulin, made by your pancreas, helps bring the glucose from your bloodstream into the cells of your body. If your bodys cells have difficulty accepting insulin, a condition called insulin resistance, or if your body cannot produce enough insulin, the glucose levels in your blood will be too high. High blood glucose can be a sign of prediabetes or diabetes. Diabetes is a serious medical issue that can damage the organs and tissues of the body if it is not controlled. By measuring how your body processes glucose, the glucose tolerance test can be used with other tests to detect or confirm prediabetes and diabetes.