"Synonyms: Apo B; Apo B100; Beta Apolipoprotein

Why It Is Done

When you have a personal or family history of heart disease and/or hyperlipidemia and your doctor is trying to determine your risk of developing cardiovascular disease. Sometimes measured to help monitor treatment for hyperlipidemia, or to help diagnose a rare Apo B deficiency.

Test Overview

Apolipoproteins are an essential part of lipid metabolism. They are component parts of lipoproteins - molecules that the body uses to transport lipids from ingested food in the intestines, throughout the bloodstream, to the liver, and to the body's cells. Apolipoproteins provide structural integrity to lipoproteins and protect the hydrophobic lipids (non-water absorbing lipids) at their center. They are recognized by receptors found on the surface of many of the body's cells and help bind lipoproteins to those cells to allow the transfer (uptake) of cholesterol and triglyceride from the lipoprotein into the cells.

There are two forms of Apolipoprotein B, Apo B-100 and Apo B-48. Apo B-48 is created in the intestines. It is an integral part of the structure of chylomicrons, large lipoproteins that are responsible for the initial transport of lipids to the liver. In the liver the body repackages the lipids and combines them with Apo B-100 (made in the liver) to form triglyceride-rich very low-density lipoproteins (VLDL). In the bloodstream an enzyme called lipoprotein lipase (LPL) removes triglycerides from VLDL to create first, intermediate density lipoproteins (IDL) and then, low density lipoproteins (LDL, - the ""bad"" cholesterol). Each VLDL particle contains one molecule of Apo B-100, which is retained as VLDL shrinks to become the more cholesterol-rich, LDL.

Apo B-100 levels are used, along with other lipid tests, to help determine an individual's risk of developing atherosclerotic heart disease and CAD. It is not used as a general population screen but may be ordered when a patient has a family history of heart disease and/or hyperlipidemia. It may be used, along with other tests, to help diagnose the cause of hyperlipidemia, especially when someone has elevated triglyceride levels (preventing accurate LDL calculations).

How To Prepare

Patient must be fasting 12 to 14 hours. "