Question: how long do you have to fast before 3 hour glucose test?
Answer: For the three-hour test: You will be asked to come to the test fasting — not having had anything to eat or drink for the previous eight hours. A fasting blood sugar will be obtained. You'll drink about 8 ounces (237 milliliters) of a glucose solution containing 3.5 ounces (100 grams) of sugar.