Preparing for Your Test

For cholesterol and glucose tests, you must fast for at least 8 hours prior to having your blood drawn, unless your doctor tells you otherwise. Fasting means no eating or drinking for at least 8 hours before the test, except water. After your blood is drawn, you may resume your regular diet.

Drink plenty of water before your blood test. This helps keep your blood pressure from dropping. The leading cause of fainting and dizziness during a blood test is a drop in blood pressure. Avoid coffee or other caffeinated drinks before your test because they actually cause your body to expel water.
Unless fasting is required for your testing, eat breakfast to help keep your blood sugar up. This will help you feel better after your blood draw and prevent light headedness and dizziness. If you think you might be nauseous during the blood draw don't eat immediately before your appointment.
If you take a blood-thinning medication, such as heparin or Coumadin (warfarin), tell the phlebotomist about these medications before your blood is drawn. After your blood is drawn, the phlebotomist will closely observe the puncture site to see that bleeding has stopped before you leave the collection location.
Relax. If you are anxious about what is going to take place, ask the person taking your blood to explain everything he or she is doing. Or think of something entirely different, like your vacation or what you are going to do after your blood test.
Eat a snack after you have your blood drawn. Take a snack with you if you will not be going directly back home or to work. That way you can eat it directly after the blood draw.
The bandage can be removed after an hour. An easy way to remove the bandage is to loosen it after a bath or shower. If the area does bleed later, apply slight pressure until the bleeding stops and apply a new bandage. Bruising may occur at the blood draw site. Do not worry if this happens. Apply some ice to the site and give it a few days to resolve.