A blood sample drawn from a vein in your arm
Lp(a) may be an independent risk factor for heart disease; i.e., patients with acceptable lipid levels but elevated Lp(a) are still at risk for heart disease. It is a lipoprotein, consisting of an LDL molecule attached to another protein, Apolipoprotein (a). In the body, Apolipoprotein (a) can interfere with the function of plasminogen (resulting in blood clot formation) and can help bind LDL molecules to artery walls (speeding up plaque formation and the narrowing and hardening of the arteries). It is this dual action that may explain the role of Lp(a) in the promotion of cardiovascular disease.
Lp(a) levels are genetically determined and will remain fairly constant in an individual over a lifetime; their levels are not affected by diet, exercise, and other typical lifestyle modifications used to lower lipid levels. They can rise a bit higher in post menopausal women. Lp(a) levels also vary by ethnicity; those patients of African American descent tend to have levels 3 to 4 times higher than Caucasians but, for reasons that are not well understood yet, they do not have a higher risk for CAD.
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 complete lipid profile, fasting for at least 12 hours may be required.
Como o exame é usado?
Lp(a) is not currently routinely ordered. It may be ordered along with other lipid tests to selectively screen for risk factors for coronary artery disease (CAD) and cerebral vascular disease. Lp(a) and several other emerging cardiac risk markers (such as Apo B, hs-CRP, Apo A, and homocysteine levels) are ordered on patients who have a strong family history of premature coronary artery disease.
Some doctors may also order these tests on patients with existing heart or vascular disease, especially those who have normal or only mildly elevated lipids. Since about 50% of the people who have heart attacks have normal cholesterol levels, doctors are starting to look at other factors that may have an influence on heart disease. It is thought that elevated Lp(a) levels can exacerbate other heart and vascular disease processes.
Quando o exame é pedido?
Lp(a) may be ordered, along with other lipid tests, when you have a family history of premature coronary artery disease and when your doctor suspects a familial hypercholesterolemia. He may also order an Lp(a) level when you have had a stroke or heart attack but have normal or only mildly elevated lipids.
In rare cases, an Lp(a) level may be ordered on a post menopausal woman to see if elevations in Lp(a) (tied to decreasing estrogen levels) have significantly increased her risk of developing CAD.
O que significa o resultado do exame?
Lp(a) levels are genetically determined and remain relatively constant over an individual's lifetime. They are not affected by lifestyle changes or by most drugs.
High Lp(a) levels may increase a person's risk for developing coronary artery disease and cerebral vascular disease and can occur in patients with a normal lipid profile. Elevated levels of Lp(a) are thought to work independently, to add to any underlying heart or vascular disease processes. Other conditions that may cause elevated levels of Lp(a) include:
- Chronic renal failure
- Estrogen depletion
- Familial hypercholesterolemia - an inherited disorder involving high levels of blood cholesterol
- Severe hypothyroidism
- Uncontrolled diabetes
- Nephrotic syndrome
Low levels of Lp(a) do not appear to cause problems.
Há mais alguma coisa que eu devo saber?
Lp(a) levels are not routinely ordered tests. A National Cholesterol Education Program (NCEP) guideline, the “Adult Treatment Panel III” (pg. II-21, available in PDF) acknowledged the possible usefulness of Lp(a) and other emerging cardiac risk tests like Lp(a), but it did not recommend them for widespread screening. The National Academy of Clinical Biochemistry (NACB) guidelines for emerging biomarkers of cardiovascular disease and stroke also recommend testing for individuals with a strong family history of premature risk of CVD or those with intermediate cardiovascular risk but not for 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) levels actually lowers risk. Experts are currently not recommending drug treatments for elevated Lp(a) levels, but some are suggesting that patients with elevated Lp(a) levels should be especially vigilant about lowering their low-density lipoprotein (LDL – the “bad” cholesterol) levels, 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, Lp(a) levels are only tested once because they are usually fairly constant. Occasionally, your doctor may order a second Lp(a) to confirm the initial level or to see if your risk has increased significantly after menopause or to monitor the effects of treatment.
Em outros sites da Internet
American Heart Association
National Academy of Clinical Biochemistry, Laboratory Medicine Practice Guidelines: Emerging Biomarkers of Cardiovascular Disease and Stroke (This is a downloadable PDF file.)
National Institutes of Health, Adult Treatment Panel III Report on High Blood Cholesterol , pg. II-21 (This is a downloadable PDF file.)