At a Glance
Why Get Tested?
To help determine your risk of developing heart disease and to monitor lipid-lowering lifestyle changes and drug therapies; to accurately determine your low-density lipoprotein cholesterol (LDL-C) level when you are not fasting
When to Get Tested?
A blood sample drawn from a vein in your arm
Test Preparation Needed?
None; however, your doctor may request that you fast.
The Test Sample
What is being tested?
The direct low-density lipoprotein cholesterol test (direct LDL-C) measures the amount of LDL cholesterol, sometimes called "bad" cholesterol, in the blood. Elevated levels of LDL-C are associated with an increased risk of hardening of the arteries (atherosclerosis) and heart disease. Usually, the amount of LDL-C is calculated using the measured values (cholesterol, HDL-C, and triglycerides) from a standard lipid profile. In most cases, this is a good estimate of the LDL-C, but it becomes less accurate with increasing triglyceride levels. Direct measurement of LDL-C is less affected by triglycerides and can be used when triglycerides are high (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.
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?
No test preparation is needed; however, a doctor may request fasting.
Ask a Laboratory Scientist
This form enables you to ask specific questions about your tests. Your questions will be answered by a laboratory scientist as part of a voluntary service provided by one of our partners, American Society for Clinical Laboratory Science. If your questions are not related to your lab tests, please submit them via our Contact Us form. Thank you.
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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
(© 1995-2010). Unit Code 200269: Direct LDL, Serum. Mayo Clinic, Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/200269 through http://www.mayomedicallaboratories.com. Accessed December 2010.
Roberts, W. (Updated April 2010). Cardiovascular Disease (Traditional Risk Markers) - Risk Markers - CVD (Traditional). ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/CVDRiskMarkerTrad.html?client_ID=LTD#tabs=0 through http://www.arupconsult.com. Accessed December 2010.
Desvigne-Nickens, P. (Updated 2009 February 2). Frequently Asked Questions, Heart Disease. U.S. Department of Health and Human Services, Office on Women's Health [On-line information]. PDF available for download at http://www.womenshealth.gov/faq/heart-disease.pdf through http://www.womenshealth.gov. Accessed December 2010.
Faix, J. (2009 Summer). Read My Lipids: LDL Cholesterol: Calculated vs. Direct. Stanford University Medical Center [On-line information]. PF available for download at http://www.stanfordlab.com/images/PDF/2009Summer.pdf through http://www.stanfordlab.com. Accessed December 2010.
Sources Used in Previous Reviews
Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.
Paxton, A. (2002 July). One Year Later, Cholesterol Guidelines Sinking In. CAP Today [On-line journal]. Available online at http://www.cap.org/captoday/archive/2002/cholesterol_guidelines_feature.html through http://www.cap.org.
Paxton, A. (2002 July). One Option For A More Complete Profile. CAP Today [On-line journal]. Available online at http://www.cap.org/captoday/archive/2002/cholesterol_guidelines_sidebar.html through http://www.cap.org.
(2001 May). ATP III At-A-Glance: Quick Desk Reference. U.S. Department Of Health And Human Services, Public Health Service, National Institutes of Health, National Heart, Lung, and Blood Institute [On-line information, NIH Publication No. 01-3305]. Available online at http://www.nhlbi.nih.gov/guidelines/cholesterol/atglance.htm through http://www.nhlbi.nih.gov.
(2002) Direct Measurement of LDL Cholesterol. The University of Iowa Department of Pathology, Laboratory Services Handbook [On-line test information]. Available online at http://www.medicine.uiowa.edu/path_handbook/lab_bulletins/archived/c2002/ldl_measured.html through http://www.medicine.uiowa.edu.
Pagana, Kathleen D. & Pagana, Timothy J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp. 602-605.
Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry, AACC Press, Washington, DC. Winter, W. and Harris, N. Chapter 21 Lipoprotein Disorders. Pp. 251-259.
Wu, A. (2006). Tietz Clinical Guide to Laboratory Tests, Fourth Edition. Saunders Elsevier, St. Louis, Missouri. Pp. 684.