Apolipoprotein B (Apo B) is the major structural apolipoprotein in VLDL (Very Low Density Lipids), LDL (Low Density Lipids) lipoproteins and chylomicron. The most important function is the transport of rich triglycerides lipoproteins from liver and intestine to other tissues. Apo B exists in two forms: Apo B-100 and Apo B-48. Apo B-100, the most important component of LDL, is synthesized in the liver and excreted in plasma as part of VLDL. Apo B-48, the most important component of chylomicrons, is synthesized in the intestine. Several studies demonstrated that in people with coronary heart disease (CHD), changes in the serum concentrations of Apo A-I and Apo B are similar to those for HDL and LDL, respectively and whereas, are somewhat better discriminators of people with CHD than the LDL and HDL cholesterol concentrations.

The hyperbetalipoproteinaemia is characterized by increased LDL Apo B-100 concentrations with normal or moderately increased concentrations of LDL cholesterol. The ratio of LDL cholesterol to Apo B-100 is therefore reduced in these patients. Defects in the Apo B structure or lipoproteins containing Apo B prevent the secretion of triglycerides rich intestinal and hepatic lipoproteins; this disorder occurs in abetalipoproteinaemia or homozygous hypobetalipoproteinaemia. Clinical diagnosis is not made on a single test result; it is done with integrated clinical and other laboratory data.