Also known as:Lipoprotein little a
Formal name:Lipoprotein (a)
Related tests:Lipid Profile, Cardiac Risk Assessment, Homocysteine, hs-CRP, Apo A-I, Apo B
Why Get Tested?
To give your health practitioner additional information about your risk of developing heart disease; as part of a targeted screen for cardiovascular disease (CVD)
When to Get Tested?
When you have a family history of CVD at a young age; when you have heart disease or have had a heart attack or stroke but your lipid profile is normal or shows only mildly elevated cholesterol and/or low-density lipoprotein cholesterol (LDL-C)
A blood sample drawn from a vein in your arm
Test Preparation Needed?
None; however, Lp(a) is often performed at the same time as a lipid profile and fasting for 9-12 hours may be required for the lipid profile.
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?
In rare cases, an Lp(a) level may be ordered when a woman is postmenopausal to see if elevations in Lp(a), tied to decreasing estrogen levels, have significantly increased her risk of developing CVD.
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.
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.
- 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?
The Lp(a) test requires specialized equipment to perform and is usually performed in a laboratory. Your sample may be sent to a reference laboratory for testing.
- If Lp(a) levels don't really change over my lifetime, why would my doctor prescribe treatment?
Although Lp(a) levels do not typically respond to treatment, if you have other additional cardiovascular risk factors, your doctor may want to treat these factors to help lower your overall risk.
© 2017 American Association for Clinical Chemistry, republished from Lab Tests Online.*
Descriptions of clinical laboratory tests were originally prepared for use on Lab Tests Online, an award-winning patient education website on clinical laboratory testing. Lab Tests Online is produced by the American Association for Clinical Chemistry (AACC), a global scientific and medical professional organization dedicated to clinical laboratory science and its application to healthcare. The Lab Tests Online website is developed in collaboration with other laboratory professional societies and is funded in part through corporate sponsorships.