Blood cholesterol is made up of a group of fats known as lipids that are necessary for cell function in the body. These lipids are produced in the liver and serve to stabilize cell membranes and make them permeable to nutrients. Cholesterol is also found in a variety of animal-based foods such as red meat and eggs. When amounts of blood cholesterol exceed normal levels, patients can be at risk of developing the disease atherosclerosis. Patients with atherosclerosis have a layer of plaque made up of cholesterol lining their blood vessels and this plaque may increase the risk of heart attack or stroke.
Lipids alone are not soluble in blood and would not be able to freely circulate throughout the body. For blood cholesterol to travel from the liver to cells and tissues of the body, it must be combined with a protein. These circulating lipoproteins carry cholesterol in either a high-density (HDL) or low-density (LDL) form. Low-density lipoproteins carry cholesterol to the cells and these are the molecules that can cause plaque to build up on the walls of blood vessels.
High-density lipoproteins have the opposite function in that they are thought to remove cholesterol from tissues and artery walls and transport it back to the liver. HDL cholesterol is often referred to as “good” cholesterol. Triglycerides are smaller fat molecules in the blood that are produced in the intestine and the liver. These molecules can also contribute to atherosclerosis.
Monitoring blood cholesterol and triglyceride levels is an important step in maintaining health. Testing should be done at least every five years in healthy patients over the age of 20 years. Patients with known high cholesterol levels should be monitored more frequently. A lipid profile can be measured on a blood sample that is taken from a patient after a 12-hour fasting. This profile will include values for total cholesterol, LDL, HDL, and triglycerides.
An optimal level of total cholesterol in a healthy patient is less than 200 milligrams per deciliter of blood (mg/dL). LDL levels should be less than 100mg/dL, while HDL levels should be greater than 40mg/dL. Triglyceride measurements in the lipid profile should be less than 150 mg/dL. For patients who maintain these levels, the risk of heart attack or stroke may be reduced.
Blood cholesterol comes from two sources. It is both manufactured in the liver and ingested during a meal. The amount of cholesterol made in the liver is determined by family history and some patients naturally produce more cholesterol than others. Patients may be able to reduce total cholesterol levels by eating a low-fat diet, getting exercise, or taking cholesterol-lowering medication prescribed by a physician.