Apo B

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Also known as: Apolipoprotein B-100; Apolipoprotein B-48
Formal name: Apolipoprotein B

At a Glance

Why Get Tested?

To help evaluate your risk of developing cardiovascular disease (CVD)

When to Get Tested?

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 CVD; sometimes measured to help monitor treatment for hyperlipidemia or to help diagnose a rare 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?

This test measures the amount of apolipoprotein B (apo B) in the blood. Apolipoproteins are the protein component of lipoproteins, complexes that transport lipids throughout the bloodstream. Apolipoproteins provide structural integrity to lipoproteins and shield the water-repellent (hydrophobic) lipids at their center.

There are two forms of apolipoprotein B: apo B-100 and apo B-48. Apo B-100 is made by the liver, while apo B-48 is produced in the intestines. Apo B-48 is an integral part of the structure of chylomicrons, large lipoproteins that are responsible for the initial transport of dietary lipids from the intestines to the liver. In the liver, the body repackages the lipids and combines them with apo B-100 to form triglyceride-rich very low density lipoprotein (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, 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 termed atherosclerosis. The atherosclerotic process 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 the triglyceride level and tends to be less reliable as triglyceride levels rise. Some labs will directly measure LDL-C levels.

Laboratory tests for apo B typically measure only apo B-100 but are often reported as simply apo B. Apo B-100 levels tend to mirror LDL-C levels. 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.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No special preparation is needed for an apolipoprotein B test. However, this test is often ordered at the same time as other tests that do require fasting, such as LDL-C, HDL-C and triglycerides. Therefore, you may be instructed to fast for 12 hours prior to having this test.

The Test

Common Questions

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Article Sources

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used in Current Review

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