At a Glance
Why Get Tested?
To help evaluate your risk of developing cardiovascular disease (CVD) and to diagnose people with specific Apo B disorders.
When to Get Tested?
This is a non-standard test currently limited mostly to hospital specialists. It can be measured when you have a personal or family history of heart disease and/or high concentrations of lipids in the blood (hyperlipidaemia) and your doctor is trying to determine your risk of developing CVD; sometimes measured to help monitor treatment for hyperlipidaemia or to help diagnose a rare apo B deficiency
A blood sample taken from a vein in your arm
Test Preparation Needed?
None; however, this test is often requested at the same time as other tests that require fasting (water only), 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 support to lipoproteins and shield the water-repellent (hydrophobic) lipids at their centre.
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 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). Apo B-100 is recognised by receptors on the surface of many of the body's cells which promote the uptake of cholesterol into the cells.
The cholesterol that LDL and apo B-100 transport is a vital component of the membranes surrounding cells and for the production of several hormones. In excess, however, LDL can lead to the formation of fatty deposits (plaques) in artery walls and the hardening and scarring of blood vessels. These fatty deposits narrow the vessels in a process termed atherosclerosis which increases the risk of heart disease and a heart attack. The LDL cholesterol (LDL-C) test is routinely requested as part of a lipid profile. The value is frequently calculated by laboratories using the concentrations of total cholesterol, high density lipoprotein cholesterol (HDL-C) and triglyceride. The calculation becomes less reliable as the triglyceride concentration rises. Rarely laboratories will directly measure LDL-C concentration.
Laboratory tests for apo B typically measure only apo B-100 but are often reported as simply apo B. Apo B-100 concentrations tend to mirror the concentration of LDL-C. Many experts think that in the future, the concentration of apo B may eventually prove to be a better indicator of risk of cardiovascular disease (CVD) than LDL-C. However, the clinical use of apo B and that of other emerging cardiac risk markers such as apo A-I, Lp(a), and hs-CRP is not 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?
Ask a Laboratory Scientist
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.