Serum lipids and lipoproteins
Few topics receive more thought than fats and lipids. Yet the answers the physician must be able to provide relative to lipids, and what the patient must do about them for best health often seem elusive.
Two major factors can account for the increased interest in lipids: (1) much improved methods for analysis of blood lipids, including cholesterol,1 triglycerides,2 and lipoproteins,3 and (2) from extensive studies in scientific centers throughout the world it has been concluded that there is a close correlation between the serum lipid levels and incidence of coronary heart disease.4 Since heart disease is a major cause of death in the United States, information concerning blood lipid levels and the institution of appropriate treatment to bring them to desirable levels are essential.
Since blood is the most readily available tissue for analysis, it is usually the material analyzed. All fats in the blood are transported bound to protein—the most rapidly metabolized fraction, a ready, and for some tissues the preferred source of energy, the free fatty acids are loosely bound to albumin. The other lipids, cholesterol, phospholipids, and triglyceride, are combined with specific polypeptides to form the lipoproteins. In normal human serum there are four major classes of lipoproteins. The chylomicra normally present in very low concentration in fasting serum are composed chiefly of triglyceride, with a very low percentage of cholesterol, phospholipid, and protein. On electrophoresis the chylomicra do not migrate from the point of application. The other three lipoprotein fractions have been named according . . .