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.
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.
This article was last reviewed on October 4, 2008.
This page was last modified on April 8, 2009.
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