The six lipids refer to total serum cholesterol, apolipoprotein A, apolipoprotein B, high-density lipoprotein, low-density lipoprotein, and triglycerides. Lipids are a general term for plasma neutral fats, triglycerides, cholesterol, lipids, phospholipids, glycolipids, sterols, and steroids. Plasma lipoproteins are macromolecular complexes composed of proteins and triglycerides, cholesterol, and phospholipids. Plasma proteins are divided into five major groups, namely celiac, very low density lipoprotein, intermediate density lipoprotein, low density lipoprotein, and high density lipoprotein. The composition and ratio of each class of lipoproteins are different, and thus their physicochemical properties, metabolic pathways and physiological functions are also different. Apolipoproteins are proteins in lipoproteins. In addition to binding to lipids to form water-soluble substances and serving as carriers for lipid transport, apolipoproteins are involved in the regulation of enzymatic activities and in the recognition and binding reactions of lipoproteins to cell membrane receptors.