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-...
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). 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.
Cholesterol 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.