LDL Cholesterol 

LDL Cholesterol 

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The standard lipid profile, as recommended by the Adult Treatment Panel III (ATP III), consists of direct measurement of total cholesterol, HDL-C, and triglycerides, with a calculated LDL-C, obtained after a 9-hour to 12-hour fast.

LDL cholesterol levels per ATP III guidelines are as follows: [1]

< 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

LDL-C is one of the major culprits in the development of atherosclerotic heart disease.

Goal LDL (to prevent atherosclerotic plaque formation) is between 50-70 mg/dL. A higher value confers increasing risk for the development of coronary artery disease and needs to be remedied. This is based on The Framingham Heart Study, which was the first study to reveal a positive association between total cholesterol and coronary artery disease (CAD). [2]

Achieving the LDL value of less than 100mg/dL is especially important in patients who have other risk factors that will accelerate the development of CAD. These risk factors are cigarette smoking, hypertension, low HDL, and a family history of CAD.

LDL-C is a calculated value and is part of the lipid profile recommended by the ATP III of the National Cholesterol Edu­cation Program (2001).

Blood is drawn after a 9-hour to 12-hour fast. The rationale behind fasting is to eliminate chylomicrons in the blood. If a patient doesn’t fast, it can cause an underestimation of the LDL value.

The sample is usually drawn in either a red-top or green- top tube and is part of the lipid profile. Early morning specimens are preferable. Patients should have been on a stable diet for 3 weeks for the results to be accurate.

Also note that in cases of recent myocardial infarction or stroke, lipid levels may be lower than what they actually are, and they normalize in 12 weeks. Checking a lipid panel 12 weeks after the acute insult is wise.

About 60-70% of cholesterol in the body is carried as low-density lipoprotein cholesterol (LDL-C) in the blood.

The standard lipid profile, as recommended by the ATP III, consists of direct measurement of total cholesterol, HDL-C, and triglycerides, with a calculated LDL-C, obtained after a 9-hour to 12-hour fast. The Friedewald formula used to calculate the LDL level in the blood is as follows:

LDL = Total cholesterol − HDL − (Triglycerides/5)

Lipoproteins are required for the transportation of cholesterol ,which in turn is required for the biosynthesis of bile acids, steroid hormones, and vitamin D.

Two main sources of cholesterol exist: One is dietary intake and the other is endogenous hepatic production.

Metabolism of ingested cholesterol yields very-low-density lipoprotein (VLDL) and intermediate density lipoprotein (IDL). Further metabolism of the VLDL results in the cholesterol rich LDL, which is the key ingredient for the development of an atherosclerotic plaque.

This test is indicated to monitor the LDL levels in order to prevent the progression of CAD.

The Friedewald formula for estimating LDL is not valid in the following 3 conditions:

Presence of chylomicrons

Triglycerides are over 400 mg/dL, and

Presence of dysbetalipoproteinemia (type III hyperlipidemia). [3]

The above 3 situations lead to an underestimation of the LDL, and a direct level is warranted.

Executive summary of the third report of the National Cholesterol Education Program (NCEP) expert panel on detection, evaluation, and treatment of high blood cholesterol in adults (Adult Treatment Panel III). JAMA. 2001. 285:2486–97.

Kannel, W.B., et al.,. Serum cholesterol, lipoproteins, and the risk of coronary heart disease. The Framingham study. Ann Intern Med,. 1971. 74(1):p. 1-12.

Rakel. Interpreting Laboratory Tests >> Separating Diseased from Disease-Free Persons. Textbook of Family Medicine,. 8th ed. Saunders; Chapter 15.

Fazia Mir, MD Fellow, Department of Gastroenterology, University of Missouri-Columbia School of Medicine

Fazia Mir, MD is a member of the following medical societies: American College of Physicians

Disclosure: Nothing to disclose.

Eric B Staros, MD Associate Professor of Pathology, St Louis University School of Medicine; Director of Clinical Laboratories, Director of Cytopathology, Department of Pathology, St Louis University Hospital

Eric B Staros, MD is a member of the following medical societies: American Medical Association, American Society for Clinical Pathology, College of American Pathologists, Association for Molecular Pathology

Disclosure: Nothing to disclose.

LDL Cholesterol 

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