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  • Total serum cholesterol greater than 200 mg/dL.
  • LDL cholesterol greater than 100 mg/dL.
  • HDL cholesterol less than 40 mg/dL.
  • Triglycerides greater than 150 mg/dL.
  • Lipoprotein(a) less than 30 mg/dL.

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Over the last decade, lipid screening has been established as a cornerstone of cardiac prevention in guidelines in primary care, cardiology, and many other specialties. Statins, inhibitors of hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase have become indispensable in the treatment of coronary artery disease (CAD) as well as in prevention of vascular events in patients at high risk, such as those with diabetes mellitus.

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Lipoproteins and Apolipoproteins

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Esterified cholesterol and triglycerides are insoluble in blood and are transported in plasma by lipoproteins. These lipoproteins are known as high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, very-low density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), and chylomicrons (Figure 2–1). Lipoproteins carry characteristic apolipoproteins in their outer layer that have functional significance (apo A-I for HDL; apo B-100 for LDL, IDL, and VLDL; and apo B-48 for chylomicrons). For example, apo B-100 is recognized by the LDL receptor and is required for hepatic production and removal of LDL. Other apolipoproteins, such as apo E and apo CI-CIII, have long been known to play an important part in lipid metabolism, while the effects of many apolipoproteins remain incompletely understood.

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Figure 2–1.
Graphic Jump Location

The density and size-distribution of the major classes of lipoprotein particles. Lipoproteins are classified by density and size, which are inversely related. HDL, high-density lipoproteins; IDL, intermediate-density lipoproteins; LDL, low-density lipoproteins; VLDL, very low-density lipoproteins. (Reproduced, with permission, from Rader DJ et al. Disorders of Lipoprotein Metabolism. In: AS Fauci, E Braunwald, DL Kasper, SL Hauser, DL Longo, JL Jameson, J Loscaizo (eds). Harrison’s Principles of Internal Medicine, 17th edition. New York: McGraw-Hill; 2008.)

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Metabolism

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Traditionally, the lipoprotein metabolism has been separated into exogenous (ie, uptake of cholesterol and fat from food) and endogenous pathways (ie, metabolic turnover in plasma, liver, and bile) (Figure 2–2). These pathways represent simultaneous events that are complementary. Key elements of dietary fat and cholesterol metabolism, and metabolism of major lipoprotein classes are discussed below.

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Figure 2–2.
Graphic Jump Location

The exogenous and endogenous lipoprotein metabolic pathways. The exogenous pathway transports dietary lipids to the periphery and the liver. The endogenous pathway transports hepatic lipids to the periphery. FFA, free fatty acids; IDL, intermediate-density lipoproteins; LDL, low-density lipoproteins; LDLR, low-density lipoprotein receptor; LPL, lipoprotein lipase; VLDL, very low-density lipoproteins.

(Reproduced, with permission, from Rader DJ et al. In: AS Fauci, E Braunwald, DL Kasper, SL Hauser, DL Longo, JL Jameson, J Loscaizo (eds). Harrison’s Principles of Internal Medicine, 17th edition. New York: McGraw-Hill; 2008.)

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Dietary Fats

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Dietary fats are processed ...

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