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Patient Test Information

Direct LDL Cholesterol

  • 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?

    As a follow-up to a lipid profile if your triglycerides are significantly elevated; at regular intervals to monitor efforts to lower LDL levels

    Sample Required?

    A blood sample drawn from a vein in your arm

    Test Preparation Needed?

    None; however, your health practitioner may request that you fast.

  • 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.

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

    No test preparation is needed; however, a health practitioner may request fasting.

  • How is it used?

    Low density lipoprotein cholesterol (LDL-C) values are typically used either to assess a person's risk for heart disease or to follow response to therapy to lower cholesterol. A standard lipid profile consists of measured values for total cholesterol, high-density lipoprotein cholesterol (HDL-C), and triglycerides. Using a mathematical equation, the amount of cholesterol present in low-density lipoprotein can be determined from the three measured values. The calculated value for LDL-C is typically reported as part of the lipid profile. When triglycerides are high, the equation is no longer valid. In this situation, the only way to accurately determine LDL-C is to measure it directly.

    High triglycerides may be due to a metabolic disorder affecting lipids. However, anyone may have high triglycerides after eating. In either situation, the direct LDL-C test can determine the amount of LDL in a person's blood.

    When is it ordered?

    Direct LDL-C is ordered whenever calculation of LDL cholesterol will not be accurate because the person's triglycerides are significantly elevated. It may be ordered by a doctor when prior test results have indicated high triglycerides. In some laboratories, this direct LDL test will automatically be performed when the triglyceride levels are too high to calculate LDL-C. This saves the doctor time by not needing to order another test, saves the patient time by not needing to have a second blood sample drawn, and speeds up the time to provide the test result.

    What does the test result mean?

    Elevated levels of LDL, as measured with the direct LDL-C test, indicate a greater risk of developing heart disease. Decreasing levels show a response to lipid-lowering lifestyle changes and/or drug therapies and indicate a decreased risk of heart disease.

    Low levels of LDL are not generally a concern and are not monitored. They may be seen in people with an inherited lipoprotein deficiency and in those with hyperthyroidism, infection, and inflammation.

    Is there anything else I should know?

    The direct LDL-C, like calculated LDL-C, should be measured when a person is healthy and "metabolically stable." Illness, surgery, trauma, a heart attack, sudden weight loss or gain, and pregnancy can all temporarily affect LDL levels.

    Why hasn't the Direct LDL-C replaced the calculated LDL-C test?

    Calculated LDL-C is about as accurate as direct LDL-C when triglyceride levels are normal. It can be done at no additional cost when a lipid profile is performed.

    Are all LDL molecules the same?

    No, LDL and other lipoprotein molecules vary in size and density. Patients with mostly small, dense LDL molecules are believed to be at greater risk for atherosclerosis than those with mostly large LDL. While it is technically possible to separate the different lipoprotein molecules by density or size and electrical charge, the clinical usefulness of information about the size distribution is unclear.

  • View Sources

    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.