The Test Sample
What is being tested?
Lipids are a group of fats and fat-like substances that are important constituents of cells and sources of energy. A lipid profile measures the level of specific lipids in the blood.
Two important lipids, cholesterol and triglycerides, are transported in the blood by lipoprotein particles. Each particle contains a combination of protein, cholesterol, triglyceride, and phospholipid molecules. The particles measured with a lipid profile are classified by their density into high-density lipoproteins (HDL), low-density lipoproteins (LDL), and very low-density lipoproteins (VLDL).
Monitoring and maintaining healthy levels of these lipids is important in staying healthy. While the body produces the cholesterol needed to function properly, the source for some cholesterol is the diet. Eating too much of foods that are high in saturated fats and trans unsaturated fats (trans fats) or having an inherited predisposition can result in a high level of cholesterol in the blood. The extra cholesterol may be deposited in plaques on the walls of blood vessels. Plaques can narrow or eventually block the opening of blood vessels, leading to hardening of the arteries (atherosclerosis) and increasing the risk of numerous health problems, including heart disease and stroke. A high level of triglycerides in the blood is also associated with an increased risk of developing cardiovascular disease (CVD), although the reason for this is not well understood.
A lipid profile typically includes:
- Total cholesterol
- High-density lipoprotein cholesterol (HDL-C) — often called "good cholesterol" because it removes excess cholesterol and carries it to the liver for removal.
- Low-density lipoprotein cholesterol (LDL-C) — often called "bad cholesterol" because it deposits excess cholesterol in walls of blood vessels, which can contribute to atherosclerosis.
For more about these, see the "The Test" tab.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm. Sometimes a drop of blood is collected by puncturing the skin on a fingertip. This fingerstick sample is typically used when a lipid profile is being measured on a portable testing device, for example, at a health fair.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
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?
Typically, fasting for 9-12 hours before having the blood sample drawn is required; only water is permitted. However, some laboratories offer non-fasting lipid profiles. In particular, children and teens may have testing done without fasting. Follow any instructions you are given and be sure to tell the person drawing your blood whether or not you have fasted.