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 " 20Reference Intervals for LDL CholesterolView LargeTABLE 16 " 20Reference Intervals for LDL Cholesterol LDL Cholesterol Level Category <100 mg/dL Optimal 100 " 129 mg/dL Near optimal/above optimal 130 " 159 mg/dL Borderline high 160 " 189 mg/dL High ≥190 mg/dL Very high
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 " 21Adult Treatment Panel III LDL-C Goals and Cutoff Points for TherapyView LargeTABLE 16 " 21Adult Treatment Panel III LDL-C Goals and Cutoff Points for Therapy Risk Category LDL-C Goal Initiate TLC Consider Drug Therapy1 High risk: CHD2 or CHD risk equivalents3 (10-y risk >20%) <100 mg/dL (optional goal: <70 mg/dL)4 ≥100 mg/dL5 ≥100 mg/dL6 (<100 mg/dL: consider drug options)1 Moderately high risk: 2+ risk factors7 (10-y risk 10 " 20%)8 <130 mg/dL9 ≥130 mg/dL5 ≥130 mg/dL (100 " 129 mg/dL; consider drug options)10 Moderate risk: 2+ risk factors7 (10-y risk <10%)8 <130 mg/dL ≥130 mg/dL ≥160 mg/dL Lower risk: 0 " 1 risk factor11 <160 mg/dL ≥160 mg/dL ≥190 mg/dL (160 " 189 mg/dL: LDL-C " lowering drug optional) 1When LDL-lowering drug therapy is employed, it is advised that intensity of therapy be sufficient to achieve at least a 30 " 40% reduction in LDL-C levels. 2Coronary heart disease (CHD) includes history of myocardial infarction, unstable angina, stable angina, coronary artery procedures (angioplasty or bypass surgery), or evidence of clinically significant myocardial ischemia. 3CHD risk equivalents include clinical manifestations of noncoronary forms of atherosclerotic disease (peripheral arterial disease, abdominal aortic aneurysm, and carotid artery disease [transient ischemic attacks or stroke of carotid origin or >50% obstruction of a carotid artery]), diabetes, and 2+ risk factors with 10-y risk for hard CHD >20%. 4Very high risk favors the optional LDL-C goal of <70 mg/dL, and in patients with high triglycerides, non " HDL-C <100 mg/dL. 5Any person at high risk or moderately high risk who has lifestyle-related risk factors (e.g., obesity, physical inactivity, elevated triglyceride, low HDL-C, or metabolic syndrome) is a candidate for therapeutic lifestyle changes to modify these risk factors regardless of LDL-C level. 6If baseline LDL-C is <100 mg/dL, institution of an LDL-lowering drug is a therapeutic option on the basis of available clinical trial results. If a high-risk person has high triglycerides or low HDL-C, combining a fibrate or nicotinic acid with an LDL-lowering drug can be considered. 7Risk factors include cigarette smoking, hypertension (BP >140/90 mm Hg or on antihypertensive medication), low HDL-C (<40 mg/dL), family history of premature CHD (CHD in male first-degree relative <55 y of age; CHD in female first-degree relative <65 y of age), and age (men ≥45 y; women ≥55 y). 8Electronic 10-y risk calculators are available at www.nhlbi.nih.gov/guidelines/cholesterol. 9Optional LDL-C goal <100 mg/dL. 10For moderately high-risk persons, when LDL-C level is 100 " 129 mg/dL, at baseline or on lifestyle therapy, initiation of an LDL-lowering drug to achieve an LDL-C level <100 mg/dL is a therapeutic option on the basis of available clinical trial results. 11Almost all people with zero or 1 risk factor have a 10-y risk <10%, and 10-y risk assessment in people with zero or 1 risk factor is thus not necessary.
Other Considerations
- The lipid profile does not measure LDL level directly but rather estimates it using the Friedewald equation:
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- 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
1National Institutes of Health, National Heart Lung and Blood Institutes National Cholesterol Education Program. http://www.nhlbi.nih.gov/about/ncep/. Accessed November 18, 2010.