A blood sample drawn from a vein in your arm
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.
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.
How is it used?
The Lp(a) test is used to identify an elevated level of lipoprotein (a) as a possible risk factor in the development of cardiovascular disease (CVD). The test may be used in conjunction with a routine lipid profile to provide additional information about a person's risk for CVD.
The Lp(a) level is genetically determined and remains relatively constant over an individual's lifetime. Since it is usually not affected by lifestyle changes or by most drugs, it is not the target of therapy. Instead, when Lp(a) is high, the presence of this added risk factor may suggest the need for more aggressive treatment of other, more treatable risk factors such as an elevated low-density lipoprotein (LDL).
When is it ordered?
Lp(a) is not routinely ordered as part of a lipid profile. However, it may be ordered, along with other lipid tests, when an individual has a strong family history of CVD at a young age that is not explained by high LDL or low HDL.
Some health practitioners may also order these tests when:
- A person has existing heart or vascular disease, especially those individuals who have healthy lipid levels or ones that are only mildly elevated
- Someone may have an inherited predisposition for high cholesterol level
- A person has had a stroke or heart attack but has normal or only mildly elevated lipids
What does the test result mean?
A high Lp(a) level may increase a person's risk for developing CVD and cerebral vascular disease. High Lp(a) can occur in people with a normal lipid profile. An elevated level of Lp(a) is thought to contribute to risk of heart disease independently of other lipids.
The level of Lp(a) is genetically determined and is not easily modified by lifestyle changes or drugs. However, some non-genetic conditions may also lead to elevated Lp(a). These include estrogen depletion, familial hypercholesterolemia, severe hypothyroidism, uncontrolled diabetes, chronic renal failure, and nephrotic syndrome.
There are no known problems associated with low Lp(a). Many individuals have no detectable Lp(a) in their blood.
Is there anything else I should know?
Lp(a) is not a routinely ordered test. A National Cholesterol Education Program (NCEP) guideline, the Adult Treatment Panel III, acknowledged the possible usefulness of Lp(a), but it did not recommend widespread screening. The National Academy of Clinical Biochemistry (NACB) guidelines for emerging biomarkers of CVD and stroke also recommend testing for individuals with a strong family history of premature atherosclerotic heart disease and/or high lipid levels (hyperlipidemia), or those with intermediate cardiovascular risk, but do not recommend general screening.
This is partially due to the fact that Lp(a) levels are genetically determined and difficult to change. Niacin and estrogen (for postmenopausal women) have been shown to lower Lp(a) levels a small amount, but their effect appears to be short-term and it is not known if lowering Lp(a) actually lowers risk. Experts are currently not recommending drug treatments for elevated Lp(a), but some are suggesting that those with elevated Lp(a) should be especially vigilant about lowering their low-density lipoprotein (LDL – the "bad" cholesterol), which may help lower their overall risk.
In general, lipids should not be measured during a fever or major infection, within four weeks of an acute myocardial infarction (heart attack), a stroke, or major surgery, right after excessive alcohol intake, with severely uncontrolled diabetes, when a woman is pregnant, or during rapid weight loss.
Why would my doctor want to order an Lp(a) more than once?
Typically, the Lp(a) level is only tested once because it is usually fairly constant. Occasionally, your doctor may order a second Lp(a) to confirm the initial level, especially if it was measured when you were ill, to see if your risk has increased significantly after menopause, or (rarely) to monitor the effects of treatment.
Can I have an Lp(a) test done in my doctor's office?
If Lp(a) levels don't really change over my lifetime, why would my doctor prescribe treatment?
On This Site
Elsewhere On The Web
American Heart Association: Coronary Artery Disease - Coronary Heart Disease
American Heart Association: Heart Attack Risk Assessment
Mayo Clinic: Blood tests for heart disease
National Heart, Lung and Blood Institute: What is a heart attack?
National Heart, Lung and Blood Institute: What is a stroke?