Back Blood-tests Explained


Apo B


At a Glance

Why Get Tested?

To help evaluate your risk of developing cardiovascular disease (CVD); sometimes to help monitor treatment for high cholesterol or to help diagnose a rare inherited apolipoprotein B (apo B) deficiency

When to Get Tested?

When you have a personal or family history of heart disease and/or high cholesterol and triglyceride levels and your health care provider is trying to determine your risk of developing CVD; sometimes on a regular basis when you are being treated for high cholesterol; rarely when your health practitioner suspects that you have an inherited apo B deficiency

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None; however, this test is often ordered at the same time as other tests that require fasting, so you may be instructed to fast for 12 hours prior to having this test.

The Test Sample

What is being tested?

Apolipoprotein B-100 (also called apolipoprotein B or apo B) is a protein that is involved in the metabolism of lipids and is the main protein constituent of lipoproteins such as very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL, the "bad cholesterol"). This test measures the amount of apo B in the blood.

Apolipoproteins combine with lipids to transport them throughout the bloodstream. Apolipoproteins provide structural integrity to lipoproteins and shield the water-repellent (hydrophobic) lipids at their center. Most lipoproteins are cholesterol- or triglyceride-rich and carry lipids through the body for uptake by cells.

Chylomicrons are the lipoprotein particles that carry dietary lipids fromthe digestive tract, via the bloodstream, to tissue – mainly the liver. In the liver, the body repackages these dietary lipids and combines them with apo B-100 to form triglyceride-rich VLDL. This combination is like a taxi full of passengers with apo B-100 as the taxi driver. In the bloodstream, the taxi moves from place to place, releasing one passenger at a time.

An enzyme called lipoprotein lipase (LPL) removes triglycerides from VLDL to produce intermediate density lipoproteins (IDL) first and then LDL. Each VLDL particle contains one molecule of apo B-100, which is retained as VLDL loses triglycerides and shrinks to become the more cholesterol-rich LDL. Apo B-100 is recognized by receptors found on the surface of many of the body's cells. These receptors promote the uptake of cholesterol into the cells.

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 (plaques) in artery walls and lead to hardening and scarring of the blood vessels. These fatty depositions narrow the vessels in a process termedatherosclerosis. The atherosclerotic process increases the risk of heart attack.

Apo B-100 levels tend to mirror LDL-C levels, a test routinely ordered as part of a lipid profile. Many experts think that apo B levels may eventually prove to be a better indicator of risk of cardiovascular disease (CVD) than LDL-C. Others disagree; they feel that apo B is only a marginally better alternative and do not recommend its routine use. The clinical utility of apo B and that of other emerging cardiac risk markers such as apo A-I, Lp(a), and hs-CRP has yet to be fully established.

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?

No special preparation is needed for an apo B test.However, since this test is often ordered at the same time as other tests that do require fasting, such as LDL-C, HDL-C and triglycerides, fasting for at least 12 hours may be required.

The Test



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