Plan to be at our office for 2-3 hours. Do not eat for 4 hours before your test. Do not smoke or chew for 4 hours before your test. Do not have any items with caffeine for 12 hours before your test, including decaf and chocolate. Do not apply lotions, powders or oils to your skin. If you are an insulin dependent patient, you should take half of your normal insulin dose the morning of the test. Drink plenty of water before the test.