Apo B
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- Also Known As:
- Apolipoprotein B-100
- Formal Name:
- Apolipoprotein B

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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 healthcare 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 care 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?
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.
You may be able to find your test results on your laboratory’s website or patient portal. However, you are currently at Testing.com. You may have been directed here by your lab’s website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab’s website or portal, or contact your healthcare practitioner in order to obtain your test results.
Testing.com is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.
The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.
If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.
Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called “normal” values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.
While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are “within normal limits.”
For more information, please read the article Reference Ranges and What They Mean.
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 from the 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 termed atherosclerosis. 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. Some recommend the measurement of apo B to help with risk prediction when a person has multiple risk factors. Other experts 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.
Common Questions
View Sources
Sources Used in Current Review
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