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Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation and prevent a hematoma (bruising). Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

Note that veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

How to Prepare for the Test

To get accurate results, you should fast for 9 to 12 hours before the test. The health care provider may advise you to discontinue drugs that can affect the test. (See "Special considerations.") You may drink water during the fast, but other beverages such as coffee, tea or soda may affect results.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:

infant test or procedure preparation (birth to 1 year)
toddler test or procedure preparation (1 to 3 years)
preschooler test or procedure preparation (3 to 6 years)
schoolage test or procedure preparation (6 to 12 years)
adolescent test or procedure preparation (12 to 18 years)

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the Test is Performed

This test is often performed to evaluate risks for heart disease.

Cholesterol is an important normal body constituent, used in the structure of cell membranes, synthesis of bile acids, and synthesis of steroid hormones. Since cholesterol is water insoluble, most serum (the noncellular portion of blood) cholesterol is carried by lipoproteins (chylomicrons, VLDL, LDL, and HDL). The term "LDL" usually means LDL-cholesterol and "HDL" means HDL-cholesterol. The term "cholesterol" usually means total cholesterol (VLDL + LDL + HDL). However, as will be discussed shortly, total cholesterol measurements are not being used as much these days to determine risk for heart disease. Chylomicrons are lipoproteins that are present shortly after a meal but disappear within about 2 hours in "normal" individuals.

Triglycerides are another component commonly measured in a lipid or cholesterol test. Triglycerides are compounds used by the body to move fatty acids (formed when fats or oils are consumed) through the blood. These fatty acids may be used by the body for energy or stored (as fat) for later use.

Excess cholesterol in the blood has been correlated with cardiovascular disease. High triglycerides are now associated with heart disease as well. LDL is sometimes referred to as "bad" cholesterol, because elevated levels of LDL correlate most directly with coronary heart disease.

HDL is sometimes referred to as "good" cholesterol since high levels of HDL reduce risk for coronary heart disease. This is because one of the main functions of HDL is to take excess cholesterol to the liver for excretion in the bile. In fact, a high HDL (defined below) will take away one risk factor you may have for coronary disease.

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