At a glance
Why get tested?
Apo B is used to help evaluate your risk of developing heart disease
When to get tested?
When you have a personal or family history of heart disease and/or and your doctor is trying to determine your risk of developing cardiovascular disease (CVD). It is sometimes measured to help monitor treatment for hyperlipidaemia to help diagnose a rare Apo B deficiency o to assist in circumstances where standard cholestrol tests are less accurate.
A blood sample drawn from a vein in your arm
Note: This test is often ordered at the same time as other tests that require fasting, such as a LDL-C (LDL-Cholesterol), HDL-C (HDL-Cholesterol) and triglycerides; therefore, you may be instructed to fast for 12 hours prior to having this test.
What is being tested?
There are actually two forms fo apolipoprotein B: Apo B-100 and Apo B-48. ApoB-48 is created in the intestines. It is an integral part of the structure of chylomicrons, large lipoproteins that are responsible for the intial transport of dietary lipids. Laboratory tests typically do not measure ApoB- 48 and only measure ApoB-100, which is often abbreviated to Apo B or apolipoprotein B.
Apo B-100 is a that is an essential part of the very low density lipoprotein (VLDL) and low density lipoprotein (LDL) complexes. Apolipoprotein B helps provide structural integrity to complexes and directs transport of the water-insoluble lipids (like cholesterol and triglycerides) in blood. Apo B is recognised by LDL receptors found on the surface of many of the body's cells. These receptors promote the uptake of cholesterol into the cells.
In the liver, the body packages lipids and combines them with Apo B-100 (made in the liver) to form triglyceride-rich VLDL. Lipoprotein lipase (LPL) is an mainly produced by adipose (fat) tissue and muscle but other tissues as well. LPL removes triglycerides from VLDL to create first, intermediate density lipoproteins (IDL) and then, low density lipoproteins (LDL - the "bad" cholesterol).
Whilst VLDL and LDL particles contain a variable amount of cholestrol, each particle contains exactly one APo B100 particle , making it a superior measure of the number of non-HDL particles than non-HDL cholestrol.
The cholesterol that LDL and Apo B-100 transport is vital for cell membrane integrity, sex hormone production, and steroid production. In excess, however, LDL can lead to fatty deposits () in artery walls and lead to hardening and scarring of the blood vessels. This narrows the coronary vessels that supply the heart (coronary artery disease or CAD) and increases the risk of heart attack. The LDL cholesterol (LDL-C) test is routinely ordered as part of a lipid profile. It is usually calculated from the total cholesterol level and tends to be less reliable as triglyceride levels rise. Some labs will directly measure LDL-C levels.
Apo B-100 levels tend to mirror LDL-C levels however, in some conditions such as Lipoprotein X, the ApoB-100 and LDL-C levels are discordant. In Lipoprotein X, routine cholestrol testing may approximate and monitor the LDL level.
Some scientists think that Apo B-100 levels may eventually prove to be a better indicator of risk of atherosclerotic heart disease than LDL-C however further studies are needed at present.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
There is no special preparation needed for an apolipoprotein B-100 test. However, this test is often ordered at the same time as other tests that do require fasting, such as a LDL-C, HDL-C and triglycerides. Therefore, the patient is often instructed to fast for 12 hours prior to having this test.