Glucose tolerance should refer to the glucose tolerance test, which is an important screening tool for diabetes and a major indicator of diabetes condition and control. Glucose tolerance test is performed in the early morning on an empty stomach after 8 hours without any calorie intake. Adults take 75 grams of anhydrous glucose orally, dissolve it in 250-300 milliliters of water, and drink it in 5-10 minutes, and then measure the venous plasma glucose in the fasting and half hour, 1 hour, 2 hours and 3 hours after the beginning of drinking the glucose water, and insulin or C-peptide levels can also be measured. The glucose tolerance test is often used to help diagnose diabetes when blood glucose is above the normal range but does not meet the diagnostic criteria for diabetes; it can also be used to help diagnose diabetes when the patient has already been diagnosed with diabetes and needs to know about the peak glucose secretion, pancreatic β-cell function, or to typify diabetes. The glucose tolerance test should be performed under the supervision of a physician.