Draw a fasting blood sample before administering glucose. Administer 75 g glucose and draw blood after two hours. The subject should remain seated throughout the test. Submit 2 mL serum or plasma for fasting and two hours. Separate serum or plasma from cells within 45 minutes of venipuncture. Label each tube with the patient's name and time interval (eg, "fasting," "two hours.") Do not label with time of day (eg, "9 AM") only.

Patient should be active and eat a regular diet that includes at least 150 grams of carbohydrate daily for three days prior to the test. Patient should be instructed not to eat or drink anything except water for at least eight hours and not more than 14 hours before the test. Patients should also be advised to discontinue, whenever possible, all nonessential medication that can affect glucose metabolism at least three days before testing.