Glucose tolerance test generally refers to the oral glucose tolerance test, and drinking water during the test may affect the accuracy of the results. Oral glucose tolerance test is a glucose load test that requires the patient to drink a certain amount of glucose after a blood draw on an empty stomach, and then have the blood drawn at 0.5 hours, 1 hour, 2 hours and 3 hours respectively after drinking, which can be used to diagnose diabetes mellitus or assess the condition. Drinking water during the test may cause dilution of the blood, resulting in an inaccurate blood glucose concentration and affecting the doctor’s judgment of the results. Patients who need an oral glucose tolerance test should follow their doctor’s instructions and should not drink large amounts of water during the test.