LDL Cholesterol

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Also known as: LDL; LDL-C
Formal name: Low-Density Lipoprotein Cholesterol

At a Glance

Why Get Tested?

To determine your risk of developing heart disease

When to Get Tested?

As part of a regular exam with a cholesterol test or lipid profile at least once every five years in adults; youth should be tested at least once between the ages of 9 and 11 and once again between the ages of 17 and 21; at regular intervals when risk factors for heart disease are present, when prior results showed high risk levels, and/or to monitor effectiveness of treatment

Sample Required?

A blood sample drawn from a vein in your arm or from a fingerstick

Test Preparation Needed?

Laboratory tests for LDL-C typically require a 12-hour fast; only water is permitted. Follow any instructions you are given.

The Test Sample

What is being tested?

Low-density lipoprotein (LDL cholesterol, LDL-C) is one type of lipoprotein that carries cholesterol in the blood. LDL-C consists mostly of cholesterol and similar substances with a small amount of protein. Most often, this test involves using a formula to calculate the amount of LDL-C in blood based on results of a lipid profile. Occasionally, LDL-C is measured directly.

Monitoring and maintaining healthy levels of lipids is important for staying healthy. Eating too much of foods that are high in cholesterol, saturated fats, and trans unsaturated fats (trans fats) or having an inherited predisposition can result in a high level of cholesterol in the blood. The extra cholesterol may be deposited in plaques on the walls of blood vessels. Plaques can narrow or eventually block the opening of blood vessels, leading to hardening of the arteries (atherosclerosis) and increased risk of numerous health problems, including heart disease and stroke.

LDL cholesterol is considered to be undesirable and is often call "bad" cholesterol because it deposits excess cholesterol in blood vessel walls and contributes to hardening of the arteries and heart disease. This is in contrast to high-density lipoproteins (HDL) that tend to transport cholesterol from the arteries to the liver. HDL is thought to protect against heart disease and so it is often called "good" cholesterol.

The LDL-C test can help determine an individual's risk of heart disease and help guide decisions about what treatment may be best if the person is at borderline or high risk. The results are considered along with other known risk factors of heart disease to develop a plan of treatment and follow up. Treatment options may involve lifestyle changes, such as diet and exercise, or lipid-lowering medications such as statins.

The results of a standard lipid profile, which consists of total cholesterol, high-density lipoprotein cholesterol (HDL-C), and triglycerides, are usually used to calculate the amount of LDL-C in the blood. The results are entered into a formula that calculates the amount of cholesterol present in LDL (see Common Questions #4). In most cases, the formula provides a good estimate of the LDL-C, but it becomes less accurate with increased triglyceride levels when, for example, a person has not fasted before having blood drawn. In this situation, the only way to accurately determine LDL-C is to measure it directly. Direct measurement of LDL-C is less affected by triglycerides and can be used when an individual is not fasting or has significantly elevated triglycerides (above 400 mg/dL).

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm. Sometimes a blood sample is collected by puncturing the skin on a fingertip. A fingerstick sample is typically used when a lipid profile is being measured on a portable testing device, for example, at a health fair.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

A calculated test result for LDL cholesterol typically requires a 12-hour fast; only water is permitted. Follow any instructions you are given.

The Test

Common Questions

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Article Sources

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used in Current Review

Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. 4th Edition, St. Louis: Mosby Elsevier; 2010, Pp 356-363.

Van Leeuwen A.M., Poelhius-Leth, D.J. Davis's Comprehensive Handbook of Laboratory and Diagnostic Tests With Nursing Implications. 3rd Edition, Philadelphia: F.A. Davis Company; 2009, Pp 325-329.

National Heart, Lung, and Blood Institute of the National Institutes of Health, United States Department of Health and Human Services. ATP III Update 2004: Implications of Recent Clinical Trials for the ATP III Guidelines. Bethesda, Md. 2004 May. Available online at http://www.nhlbi.nih.gov/guidelines/cholesterol/atp3upd04.htm through http://www.nhlbi.nih.gov.

(Updated 2011 August 2). Mayo Clinic. High Cholesterol [Online Information]. Available online at http://www.mayoclinic.com/health/high-blood-cholesterol/DS00178 through http://www.mayoclinic.org. Accessed August 2011.

(Updated 2010 May 23). MedlinePlus Medical Encyclopedia. LDL Test [Online information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003495.htm through http://www.nlm.nih.gov. Accessed August 2011.

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(November 2012) American Association of Family Physicians. High Cholesterol. Available online at http://familydoctor.org/familydoctor/en/diseases-conditions/high-cholesterol.html through http://familydoctor.org. Accessed October 2012.

Kavey R-EW, et al. Expert panel on integrated guidelines for cardiovascular health and risk reduction in children and adolescents: Summary report. Pediatrics 2011; 128: DOI:10.1542/peds.2009-2107C. PDF available for download at http://pediatrics.aappublications.org/site/misc/2009-2107.pdf through http://pediatrics.aappublications.org. Accessed October 2012.

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KidsHealth.org. Cholesterol and Your Child. Available online at http://kidshealth.org/parent/medical/heart/cholesterol.html# through http://kidshealth.org. Accessed October 2012.

(2006) Sekar K. Increased Small Low-Density Lipoprotein Particle Number, A Prominent Feature of the Metabolic Syndrome in the Framingham Heart Study. Circulation. Available online at http://circ.ahajournals.org/content/113/1/20.full through http://circ.ahajournals.org. Accessed October 2012.

(September 23, 2002) Blake G, et al. Low-Density Lipoprotein Particle Concentration and Size as Determined by Nuclear Magnetic Resonance Spectroscopy as Predictors of Cardiovascular Disease in Women. Circulation, Available online at http://circ.ahajournals.org/content/106/15/1930.full throughhttp://circ.ahajournals.org. Accessed October 2012.

Blakenstein R, et al. Predictors of Coronary Heart Disease Events Among Asymptomatic Persons With Low Low-Density Lipoprotein Cholesterol. Journal of the American College of Cardiology Volume 58, Issue 4, 19 July 2011, Pp 364–374.

Krauss R. Lipoprotein subfractions and cardiovascular disease risk. Curr Opin Lipidol 2010 Aug;21(4):305-11. Abstract available online at http://www.ncbi.nlm.nih.gov/pubmed/20531184 through http://www.ncbi.nlm.nih.gov. Accessed October 2012. 

Prado K, et al. Low-density lipoprotein particle number predicts coronary artery calcification in asymptomatic adults at intermediate risk of cardiovascular disease. J Clin Lipidol 2011 Sep-Oct;5(5):408-13. Abstract available online at http://www.ncbi.nlm.nih.gov/pubmed/21981843 through http://www.ncbi.nlm.nih.gov. Accessed October 2012.

(May 2012) Lavie C, et.al. To B or Not to B: Is Non–High-Density Lipoprotein Cholesterol an Adequate Surrogate for Apolipoprotein B? Mayo Clin Proc. 2010 May; 85(5): 446–450. Available online at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2861974/ through http://www.ncbi.nlm.nih.gov. Accessed October 2012.

Sources Used in Previous Reviews

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American Heart Association. "What are healthy levels of cholesterol?" Available online at

National Heart, Lung, and Blood Institute of the National Institutes of Health, United States Department of Health and Human Services. Third report of the National Cholesterol Education Program (NCEP) Expert Panel on detection, evaluation, and treatment of high blood pressure in adults (Adult Treatment Panel III). Bethesda, Md. 2001 May. Available online at http://www.nhlbi.nih.gov/guidelines/cholesterol/atp3_rpt.htm through http://www.nhlbi.nih.gov.

American Heart Association. "Numbers That Count for a Healthy Heart." Available online at http://www.americanheart.org.

Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. 3rd Edition, St. Louis: Mosby Elsevier; 2006 pp 351-357.

National Heart, Lung, Blood Institute. National Cholesterol Education Program Guidelines, Cholesterol, ATP III (online information). Available online at http://www.nhlbi.nih.gov. Accessed February 2008.

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American Academy of Pediatrics. 7 Jul 2008. AAP issues new guidelines on cholesterol screening (press release). Available online at http://www.aap.org/new/july08lipidscreening.htm through http://www.aap.org. Accessed August 2008.