Prepare for your Advanced Vitamins Blood Test by following these instructions. Do not eat for 12 hours prior to your test. Drink plenty of water, if you take medication then you are allowed to take it as you would normally. You should take this test before you take any medication or vitamin/mineral supplements. Do not take biotin supplements for two days before this test, discuss this with your doctor if it is prescribed. Do not take vitamin B12 for two weeks prior to this test. If your B12 is prescribed ask your doctor whether to stop. Wrap your sample in foil immediately after it is taken.