For OGTT
DO NOT eat or drink anything (other than sips of water) for 8 to 14 hours before your test. (You also cannot eat during the test.)
You will be asked to drink a liquid that contains glucose, 100 grams (g) .
You will have blood drawn before you drink the liquid, and again 3 more times every 60 minutes after you drink it. Each time, your blood glucose level will be checked.
Allow at least 3 hours for this test.