At a Glance
Why Get Tested?
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 to Get Tested?
When you have high cholesterol and triglycerides (hyperlipidemia) and/or a family history of CVD; when your health care 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
Test Preparation Needed?
None; however, this test is often ordered at the same time as other tests that require fasting, so you may be instructed to fast for 12 hours prior to having this test.
The Test Sample
What is being tested?
Apolipoprotein A-I (apo A-I) is a protein that has a specific role in the 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.
Apolipoproteins combine with lipids to transport them 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 and carry lipids 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 into bile. HDL's reverse transport is the only way that cells can get rid of excess cholesterol. It 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.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm. As an alternative, particularly in pediatric care, the blood sample is obtained by pricking the heel or fingertip.
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 complete lipid profile, fasting for at least 12 hours may be required.
Ask a Laboratory Scientist
Form temporarily unavailable
Due to a dramatic increase in the number of questions submitted to the volunteer laboratory scientists who respond to our users, we have had to limit the number of questions that can be submitted each day. Unfortunately, we have reached that limit today and are unable to accept your inquiry now. We understand that your questions are vital to your health and peace of mind, and recommend instead that you speak with your doctor or another healthcare professional. We apologize for this inconvenience.
This was not an easy step for us to take, as the volunteers on the response team are dedicated to the work they do and are often inspired by the help they can provide. We are actively seeking to expand our capability so that we can again accept and answer all user questions. We will accept and respond to the same limited number of questions tomorrow, but expect to resume the service, 24/7, as soon as possible.
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Sources Used in Current Review
Elhomsy, G and Griffing, G. (Updated 2012 August 31). Apolipoprotein A-I. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/2087313-overview through http://emedicine.medscape.com. Accessed March 2014.
Delgado, J. et. al. (Updated 2014 February). Cardiovascular Disease (Non-traditional Risk Markers) - Risk Markers - CVD (Non-traditional) ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/CVDRiskMarkerNontrad.html?client_ID=LTD through http://www.arupconsult.com. Accessed March 2014.
(© 1995–2014). Apolipoprotein A1, Plasma. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/80309 through http://www.mayomedicallaboratories.com. Accessed March 2014.
Lam, J. (Revised 2012 September) Atherosclerosis. Merck Manual for Healthcare Professionals [On-line information]. Available online through http://www.merckmanuals.com. Accessed March 2014.
Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 112-115.
Clarke, W., Editor (© 2011). Contemporary Practice in Clinical Chemistry 2nd Edition: AACC Press, Washington, DC. Pp 288-289.
McPherson, R. and Pincus, M. (© 2011). Henry's Clinical Diagnosis and Management by Laboratory Methods 22nd Edition: Elsevier Saunders, Philadelphia, PA. Pp 240.
Sources Used in Previous Reviews
Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.
ARUP's Guide to Clinical Laboratory Testing (CLT). Apolipoprotein A-1 [On-line information]. Available online at http://www.arup-lab.com/guides/clt/tests/clt_al67.htm#1142700 through http://www.arup-lab.com.
Theoretical Biophysics Group (2001 February 19, Modified). HDL and Apo A-1 Structure Prediction. NIH Resource for Macromolecular Modeling and Bioinformatics [On-line information]. Available online at http://www.ks.uiuc.edu/Research/apoa1/ through http://www.ks.uiuc.edu.
Hargrove, G.M., Junco, A., and Wong, N.C.W. (1999). Hormonal regulation of apolipoprotein AI. Journal of Molecular Endocrinology 22, 103-111 [On-line Journal]. PDF available for download at http://journals.endocrinology.org/jme/022/0103/0220103.pdf through http://journals.endocrinology.org.
(2000 March). What Are Cholesterol, Other Lipids, And Lipoproteins? Northern Berkshire Health Systems, Health A to Z [Well-Connected Online report]. Available online at http://www.nbhealth.org/myhealthadviser/atoz/doc23.html through http://www.nbhealth.org.
Pagana, Kathleen D. & Pagana, Timothy J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO., Pp 110-114.
Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry, AACC Press, Washington, DC. Winter, W. and Harris, N. Chapter 21: Lipoprotein Disorders, Pp 251-259.
O'Riordan, M. (2007 March 22). High Levels of Apolipoprotein A1 and HDL Associated With Reduced Risk of Recurrent VTE. Heartwire - a professional news service of WebMD [On-line information]. Available online at http://www.medscape.com/viewarticle/554016 through http://www.medscape.com.
Kasper DL, Braunwald E, Fauci AS, Hauser SL, Longo DL, Jameson JL eds, (2005). Harrison's Principles of Internal Medicine, 16th Edition, McGraw Hill.
Benderly, M. et. al. (2009 February 16). Apolipoproteins and Long-Term Prognosis in Coronary Heart Disease Patients. Medscape from American Heart Journal. 2009;157(1):103-110 [On-line information]. Available online at http://www.medscape.com/viewarticle/585982 through http://www.medscape.com. Accessed July 2010.
(© 1995–2010). Unit Code 80309: Apolipoprotein A1, Plasma. Mayo Clinic, Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/80309 through http://www.mayomedicallaboratories.com. Accessed July 2010.
Delgado, J. et. al. (Updated 2010 April). Cardiovascular Disease (Non-traditional Risk Markers) - Risk Markers - CVD (Non-traditional). ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/CVDRiskMarkerNontrad.html?client_ID=LTD# through http://www.arupconsult.com. Accessed July 2010.
O'Riordan, M. (2007 March 22). High Levels of Apolipoprotein A1 and HDL Associated With Reduced Risk of Recurrent VTE. Medscape Today [On-line information]. Available online at http://www.medscape.com/viewarticle/554016 through http://www.medscape.com. Accessed July 2010.
Myers, G. Editor (2009). Emerging Biomarkers for Primary Prevention of Cardiovascular Disease and Stroke. The National Academy of Clinical Biochemistry Laboratory Medicine Practice Guidelines [On-line information]. PDF available for download at http://www.aacc.org/members/nacb/LMPG/OnlineGuide/PublishedGuidelines/risk/Documents/EmergingCV_RiskFactors09.pdf through http://www.aacc.org/members/nacb/LMPG. Accessed July 2010.
Pagana, K. D. & Pagana, T. J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 110-114.
Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 142-145.
Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER, Bruns DE, eds. St. Louis: Elsevier Saunders; 2006 Pp 916-917, 928-934.