Low-density lipoprotein, or LDL, is a form of cholesterol that is measured, along with high-density lipoprotein, or HDL and triglycerides, to determine risk levels for cardiovascular disease. The purpose of LDL is to transport cholesterol and triglyceride molecules from the liver, where they are produced, to the cells around the body for use in constructing cell membranes, and in hormones and fat soluble vitamins.
LDL Level
LDL is the form of cholesterol that, when present in excess, can lead to atherosclerosis and cardiovascular disease. LDL is usually measured in the blood,after a 12-hour fast. The American Heart Association advises that a desirable level of LDL is under 100 milligrams per deciliter, or mg/dL, up to 129 mg/dL is optimal, and above 130 mg/dL represents increased risk.
Total Cholesterol to LDL Ratio
The ratio of HDL to LDL gives some added perspective on overall risk. Elevated total cholesterol, which is the sum of LDL and HDL, in the presence of high levels of HDL may confer some protective benefit, since HDL is beneficial by its removal of excess LDL from circulation. The website ExRx reports that for men, a ratio of 3.6:1.0 or less is desirable, while for women, a ratio of 3.2:1.0 or below is recommended.
LDL to HDL ratio
The ratio of LDL to HDL cholesterol, comparing the "bad" directly with the "good," produces a value that, like the total cholesterol to LDL ratio, gives a broader picture than absolute values alone. A ratio of 3.5:1.0, or below, is the target for this ratio, according to the website Emedtv, implying that there is enough HDL to offset the potential harmful effects of the LDL.
LDL Particle Size
Within the category of LDL cholesterol is a range of sizes of LDL molecules. Small LDL molecules, which contain the same amount of protein but fewer lipids, are associated with atherosclerosis because they more readily penetrate the linings of arteries than their larger counterparts, thereby initiating plaque formation, according to the February 2002 Journal of the American Medical Association. A study known as the Stanford City Project showed that the presence of small, dense LDL was associated with three times greater risk for heart attack, as reported in the Croatian Medical Journal. Tests to determine LDL particle size have been devised based on the magnetic and electrical properties of the molecules, or also by high speed centrifuge to separate them, according to Johns Hopkins research.
Oxidized LDL
Part of the process of atherosclerotic plaque formation has to do with LDL that has become oxidized. When oxidized LDL particles are engulfed by macrophages in the linings of arteries, the resulting cell is called a foam cell. Foam cells in certain locations initiate the inflammatory process, attracting platelets and other types of molecules to the site which accumulate and add to the plaques, according to the January 2008 journal Cardiovascular Research. Measurement of oxidized LDL along with other lipid parameters, can be helpful in evaluating cardiovascular risk, and commercial blood tests are available.
References
- Journal of the American Medical Association: Is the Size of Low-Density Lipoprotein Particles Related to the Risk of Coronary Heart Disease?
- Croatian Medical Journal: Low Density Lipoprotein Particle Size Phenotyping in Healthy Persons and Patients with Myocardial Infarction
- Johns Hopins Health Alerts: The New Blood Lipid Tests -- Sizing Up LDL Cholesterol
- Cardiovascular Research: Platelet lipoprotein interplay: trigger of foam cell formation
- American Heart Association: Levels of Cholesterol
