The Test Sample
What is being tested?
Lipoprotein (a) or Lp(a) is one type of lipoprotein that carries cholesterol in the blood. It is similar to low-density lipoprotein (LDL, the "bad" cholesterol) in that it contains a single apolipoprotein B protein along with cholesterol and other lipids. This test measures the amount of Lp(a) in the blood to help evaluate a person's risk of developing cardiovascular disease (CVD).
Like LDL, Lp(a) is considered a risk factor for CVD. The amount of Lp(a) that a person has is genetically determined and remains relatively constant over an individual's lifetime. A high level of Lp(a) is thought to contribute to a person's overall risk of CVD, making this test potentially useful as a cardiovascular risk marker.
The protein portion of Lp(a) consists of:
- Apolipoprotein B (Apo B) – a protein that is involved in the metabolism of lipids and is the main protein constituent of lipoproteins such as LDL and very low-density lipoprotein (VLDL)
- Apolipoprotein(a) – A second protein component, called apolipoprotein(a), which is attached to the Apo B. Apolipoprotein(a) has an unusual structure and is thought to inhibit clots from being broken down normally. The size of the apolipoprotein(a) portion of Lp(a) varies in size from person to person and tends to be smaller in Caucasians than in those of African ancestry. The significance of the variation in size in contributing to CVD risk is complex, but there is some evidence that smaller size increases risk. Most Lp(a) tests do not measure the size of apolipoprotein(a), however. They measure and report only the level of Lp(a) in blood.
Since about 50% of the people who have heart attacks have a normal cholesterol level, researchers have sought other factors that may have an influence on heart disease. It is thought that Lp(a) may be one such factor. Lp(a) has two potential ways to contribute. First, since Lp(a) can promote the uptake of LDL into blood vessel walls, it may promote the development of atherosclerotic plaque on the walls of blood vessels. Secondly, since apo(a) has a structure that can inhibit enzymes that dissolve clots, Lp(a) may promote accumulation of clots in the arteries. For these reasons, Lp(a) may be more atherogenic than LDL.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
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?
No test preparation is needed; however, since this test may be performed at the same time as a lipid profile, fasting for 9-12 hours may be required.