Cholesterol, Low-Density Lipoprotein (LDL)

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Subject: Cholesterol, Low-Density Lipoprotein (LDL)

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Definition

  • LDL cholesterol, also known as LDL-C, is produced by the metabolism of VLDL cholesterol and consists of mostly cholesterol, protein, and phospholipids that carry cholesterol in the bloodstream from the liver to the peripheral tissues. LDL-C is termed the “bad cholesterol,” and LDL-C levels are associated with atherosclerosis and coronary heart disease.

  • Normal range: see Table 16.20.

 
TABLE 16–20
Reference Intervals for LDL Cholesterol

Use

  • To determine risk of heart disease and atherosclerosis. LDL-C is calculated when ordered in combination with total cholesterol, HDL cholesterol, and triglycerides as a lipid profile.

Interpretation

Increased In

  • Familial hypercholesterolemia

  • Nephrotic syndrome

  • Hepatic disease

  • Hepatic obstruction

  • Chronic renal failure

  • Hyperlipidemia types II and III

  • DM

Decreased In

  • Abetalipoproteinemia

  • Hyperthyroidism

  • Tangier disease

  • Hypolipoproteinemia

  • Chronic anemia

  • Lecithin cholesterol acyltransferase deficiency

  • Apo C-II deficiency

  • Hyperlipidemia type I

Limitations

  • LDL-C values may be high because of a diet high in saturated fats and cholesterol, pregnancy, or use of steroids.

  • LDL values should be measured only on fasting samples.

  • LDL cholesterol may be decreased because of acute stress, recent illness, and estrogens.

  • Other factors that may affect LDL-C values: cigarette smoking, hypertension (blood pressure >140/90 mm Hg or taking antihypertensive medication), family history of premature CHD (CHD in male first-degree relative <55 years; CHD in female first-degree relative <65 years), and age (men >45 years; women >55 years). See Table 16.21 for additional information.

  • At this time, there are no specific recommendations on the routine measurement of LDL particle size and number.

 
TABLE 16–21
Adult Treatment Panel III LDL-C Goals and Cutoff Points for Therapy

Other Considerations

  • The lipid profile does not measure LDL level directly but rather estimates it using the Friedewald equation:

  • Note: The formula is only valid from a fasting specimen, and triglycerides must be <400 mg/dL.

  • LDL-C can be measured directly when the triglycerides are elevated.

Suggested Reading

National Institutes of Health, National Heart Lung and Blood Institute's National Cholesterol Education Program. http://www.nhlbi.nih.gov/about/ncep/. Accessed November 18, 2010.
 
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