High values have been traditionally considered as those in the 90th and 95th percentiles low values were considered to be those below the 5th percentile. Since the levels of plasma lipids have a bell-shaped distribution in the general population, the definition of either a high or a low value of these substances has remained an arbitrary statistical decision. Plasma lipoproteins are separated by hydrated density electrophretic mobility size and their relative content of cholesterol, triglycerides, and protein into five major classes: chylomicrons, very-low-density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL). Triglycerides are fatty acid esters of glycerol and represent the main lipid component of dietary fat and fat depots of animals.Ĭholesterol and triglycerides, being nonpolar lipid substances (insoluble in water), need to be transported in the plasma associated with various lipoprotein particles. It is also a precursor of various critical substances such as adrenal and gonadal steroid hormones and bile acids. Cholesterol is an unsaturated alcohol of the steroid family of compounds it is essential for the normal function of all animal cells and is a fundamental element of their cell membranes.
Cholesterol, triglycerides, and high-density lipoproteins are important constituents of the lipid fraction of the human body.