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:
Help diagnose inherited or acquired conditions that cause apo A-I deficiencies
Monitor the effectiveness of lifestyle changes and lipid treatments
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 health 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 health 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 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.
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. For more on some of these disorders, see the Related Pages tab.
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.
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. Health 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.
This article was last reviewed on April 29, 2014. | This article was last modified on April 29, 2014.
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