To determine whether or not you have an adequate level of apo A-I, especially if you have a low level of high-density lipoprotein (HDL-C), and to help determine your risk of developing cardiovascular disease (CVD)
When you have a low value of HDL-C, high cholesterol and triglycerides (hyperlipidemia), and/or a family history of CVD; when your healthcare provider is trying to assess your risk of developing heart disease; when monitoring the effectiveness of lipid treatment and/or lifestyle changes
A blood sample drawn from a vein in your arm; blood from the prick of a baby's heel or finger
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.
Apolipoprotein A-I (apo A-I) is a protein that has specific roles in the transportation and metabolism of lipids and is the main protein component in high-density lipoprotein (HDL, the "good cholesterol"). This test measures the amount of apo A-I in the blood.
Lipids alone cannot dissolve in the blood; they are like oil that floats on water. Apolipoproteins are the proteins that combine with lipids to make lipoprotein particles that can transport lipids throughout the bloodstream. Apolipoproteins provide structural integrity to lipoproteins and shield the water-repellent (hydrophobic) lipids at their center.
Most lipoproteins are cholesterol- or triglyceride-rich (two main lipids) and carry them throughout the body for uptake by cells. HDL, however, is like an empty taxi. It goes out to the tissues and picks up excess cholesterol, then transports it back to the liver. In the liver, the cholesterol is either recycled for future use or excreted in bile. HDL's reverse transport is the only way that cells can get rid of excess cholesterol. This reverse transport helps protect the arteries and, if there is enough HDL present, it can even reverse the build-up of fatty plaques, deposits resulting from atherosclerosis that can lead to cardiovascular disease (CVD).
Apolipoprotein A is the taxi driver. It activates the enzymes that load cholesterol from the tissues into HDL and allows HDL to be recognized and bound by receptors in the liver at the end of the transport. There are two forms of apolipoprotein A: apo A-I and apo A-II. Apo A-I is found in greater proportion than apo A-II (about 3 to 1). The concentration of apo A-I can be measured directly and tends to rise and fall with HDL levels. Deficiencies in apo A-I correlate with an increased risk of developing CVD. Apo A-I levels provide more information to help evaluate CVD risk, especially when HDL levels are low.
Apolipoprotein A-I (apo A-I) may be ordered, along with other lipid tests, as part of a profile to help determine a person's risk of developing cardiovascular disease (CVD). It may be used as an alternative to a high-density lipoprotein (HDL) test, but it is not generally considered "better" or more informative than HDL and is not ordered routinely.
Apo A-I is a protein that has a specific role in the metabolism of lipids and is the main protein component in HDL, the "good cholesterol". HDL removes excess cholesterol from cells and takes it to the liver for recycling or disposal. Levels of apo A-I tend to rise and fall with HDL levels, and deficiencies in apo A-I correlate with an increased risk of developing CVD.
An apo A-I test may sometimes be ordered to:
An apo A-I may be ordered along with an apolipoprotein B (apo B) test to determine an apo B/apo A-I ratio. This ratio is sometimes used as an alternative to a total cholesterol/HDL ratio (sometimes reported as part of a lipid profile) to evaluate risk for developing CVD.
Apo A-I may be measured when someone has a personal or family history of abnormal lipid levels and/or premature CVD. It may be ordered when a healthcare practitioner is trying to determine the cause of a person's high cholesterol and/or suspects it may be due to a disorder that is causing a deficiency in apo A-I.
Apo A-I may be ordered along with apo B when a healthcare practitioner wants to check an apo B/apo A-I ratio as a CVD risk indicator, to evaluate the "bad" to "good" cholesterol.
Apo A-I may be ordered, along with other tests, when someone has undergone lipid-lowering treatment or lifestyle changes, such as decreased dietary fat and increased regular exercise, to monitor the effectiveness of the changes.
Low levels of apo A-I are usually associated with low levels of HDL and impaired clearance of excess cholesterol from the body. Low levels of apo A-I, along with high concentrations of apo B, are associated with an increased risk of cardiovascular disease. High levels of apo A-I is considered protective and can be independent of HDL levels.
There are some genetic disorders that lead to deficiencies in apo A-I (and therefore to low levels of HDL). People with these disorders tend to have abnormal lipid levels, including high levels of low-density lipoprotein (LDL – the "bad" cholesterol). Frequently, they have accelerated rates of atherosclerosis. These genetic disorders are primary causes of low apo A-I.
Changes in levels of apo A-I may also be associated with other factors. Some of the conditions that contribute to decreases or increases in apo A-I are listed below.
Apo A-I may decrease with:
Apo A-I may increase with:
The concentration of apo A-I reflects the amount of HDL in the serum. Since women tend to have higher HDL, they also have higher levels of apo A-I.
The apo A-I test is not routinely ordered. Healthcare practitioners still have to determine the best uses for the apo A-I and other tests for emerging cardiac risk markers (such as apo B, hs-CRP, and Lp(a)). They offer additional information in specific situations but are not meant to replace the lipid tests already routinely available.
Behaviors that tend to raise HDL also raise apo A-I. Regular exercise is one of the best ways to raise HDL and apo A-I. By decreasing the saturated fat in your diet, maintaining a healthy weight, and exercising, you can help decrease your risk of developing heart disease.
No, the apo A-I test requires specialized equipment and is not offered by every laboratory. Your blood may need to be sent to a reference laboratory for testing.
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