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You need to know about the specific blood tests your doctor is ordering. Some blood tests will require special preparation to get accurate results. Some examples of common blood tests which require special preparation include:  Glucose tolerance tests, which require fasting prior to coming to the lab. You also have to remain at the lab for up to 5 hours and your blood is taken every 30 to 60 minutes. Fasting Glucose test, which is done after you have not eaten or had anything to drink except water for 8 to 12 hours. These tests are often first thing in the morning so you aren’t asked to go without eating all day. Serum Lipid testing, also called a cholesterol test, which will sometimes require you to fast for 9 to 12 hours before the test.  Cortisol blood test, where you are asked to refrain from exercising the day before, lie down for 30 minutes before the test, and refrain from eating or drinking for 1 hour before the test. There are certain substances that can alter blood tests, which you may need to stop before your blood test. Prescription medications, recreational drugs, alcohol intake, vitamins, blood thinners, or over-the-counter medications can often change the results of a blood test, depending on what the blood test is for. Your physician can determine if you should wait 24 to 48 hours to have the blood work done or if what you have taken will not significantly alter the blood test results. There are some blood tests that can be compromised based on your activities. These tests can be altered by recent physical activity or heavy exercise, undergoing dehydration, smoking, drinking herbal teas, or sexual activity. You might be asked to refrain from some of these activities prior to taking a blood test. Many tests do not require special preparation prior to getting your blood drawn. However, when in doubt, ask. If your physician does not give you any special instructions, it is important that you ask in order to reduce the potential that you arrive for the test without preparing sufficiently. Being sufficiently hydrated makes the blood draw easier. The veins will be bigger and easier to find and the blood is not as thick and flows into the tube easier. If you need to fast from water as well, be sure you are very hydrated from the day before. This may mean needing to get up during the night to urinate. However, being well hydrated will make your blood test easier. Before you get ready to take a blood test, warm the extremity where the blood will be drawn. Use a warm compress over the area for 10 to 15 minutes to improve the blood flow to that area. Wear warmer than normal clothes for the season when you go in to get your blood drawn. This increases your skin temperature, increases the blood flow to the area, and makes it easier for the phlebotomist (the person who draws your blood) to find a good vein. If you deviated from the instructions given to you to prepare for the blood test prior to having your blood drawn, you need to notify the person who will draw your blood when you arrive. If the deviation is significant enough to alter the results of the test, you may have to return to have the blood test drawn another day. Mention if you are allergic to latex or latex sensitive. Latex is in many types of gloves and band-aids, which are used while taking blood. Some people have an allergy or sensitivity to latex which can be life threatening. If you know that you have either an allergy or sensitivity, it is important to notify both your doctor and the phlebotomist so they can use latex-free equipment.

Summary:
Talk with your doctor. Discuss your medications. Refrain from certain activities. Ask your doctor for instructions. Drink enough water. Warm your extremities. Talk to the phlebotomist.