This test measures the amount of apolipoprotein B100 (apoB100) in the blood.

Lipoproteins are large complexes of molecules that transport lipids (primarily triglycerides and cholesterols) through the blood. Apolipoproteins are proteins on the surface of the lipoprotein complex that bind to specific enzymes or transport proteins on the cell membranes; this directs the lipoprotein to the proper site of metabolism. ApoB100 is in an intermediate form of lipoprotein (IDL) and an low density lipoprotein (LDL).

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 cause veins below the tourniquet to distend (fill with blood).

A needle is inserted into the vein, and the blood is collected in an airtight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

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.

• 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)

Most often, this test is performed to help determine the cause of hyperlipidemia (elevated blood lipid levels).

ApoB100 is a form of apoB that occurs in LDL and IDL but not in chylomicrons (large lipoprotein particles that contain apoB48 and other apolipoproteins).

Elevated levels of apoB occur in familial combined hyperlipidemia and acquired hyperlipidemia (elevated blood lipid levels). ApoB100 measurements can help to determine the specific type or cause of hyperlipidemia.

Other disorders that may be associated with elevated apoB levels include angina pectoris and heart attack.

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)
• Multiple punctures to locate veins

Apolipoprotein levels can be measured directly, unlike HDL and LDL measurements, which are indirect. This test may give a much more accurate picture of your health, including your risk for heart disease.

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 others.