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 When triglycerides are high, the equation is no longer valid.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.
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.
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.
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.
This article was last reviewed on January 13, 2011. | This article was last modified on November 15, 2013.
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