At a Glance
Why Get Tested?
To determine risk of developing heart disease
When to Get Tested?
A blood sample drawn from a vein in the arm or from a fingerstick
Test Preparation Needed?
Laboratory tests for LDL-C generally require a 12-hour fast; only water is permitted.
The Test Sample
What is being tested?
LDL is a type of lipoprotein that carries cholesterol in the blood. LDL is considered to be undesirable because it deposits excess cholesterol in walls of blood vessel and contributes to hardening of the arteries (atherosclerosis) and heart disease. Hence LDL cholesterol is often termed “bad” cholesterol.
Usually, the amount of LDL cholesterol (LDL-C) is calculated using the results of a standard lipid profile, which consists of total cholesterol, high-density lipoprotein cholesterol (HDL-C), and triglycerides. By applying a formula, the amount of cholesterol present in low-density lipoprotein can be determined, and this calculated value is typically reported as well. In most cases, this is a good estimate of the LDL-C, but it becomes less accurate with increased triglyceride levels when, for example, you have not fasted before having your 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 you are not fasting or when you have significantly elevated triglycerides (above 400 mg/dl).
How is the sample collected for testing?
The test for LDL cholesterol uses a blood sample. Most often, the blood sample is collected by venipuncture (using a needle to collect blood from a vein). LDL cholesterol can also be determined from blood collected by puncturing the skin on a finger. 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 requires a 12 hour fast; only water is permitted.
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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. 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.
Henry’s Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2007.
Falko JM, Moser RJ, Meis SB, Caulin-Glaser T. Cardiovascular disease risk of type 2 diabetes mellitus and metabolic syndrome: focus on aggressive management of dyslipidemia. Curr Diabetes Rev. 2005 May;1(2):127-35.
Hayashi T, et. al. Importance of Lipid Levels in Elderly Diabetic Individuals—Baseline Characteristics and 1-Year Survey of Cardiovascular Events. Cir J 2008; 72:218—225.
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.
Sources Used in Previous Reviews
Thomas, Clayton L., Editor (1997). Taber’s Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
American Heart Association. "What are healthy levels of cholesterol?" Available online at http://126.96.36.199/presenter.jhtml?identifier=183.
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.