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Apolipoprotein A-I 

  • Author: Georges Elhomsy, MD; Chief Editor: Eric B Staros, MD  more...
 
Updated: Nov 21, 2014
 

Reference Range

Apolipoprotein A-I (Apo-A1) is a structural and functional protein that constitutes approximately 70% of the protein in high density lipoprotein (HDL).

The reference range of Apo-A1 varies by sex, as follows:

  • Men: Greater than 120 mg/dL (1.2 g/L)
  • Women: Greater than 140 mg/dL (1.4 g/L)

levels decrease with age.

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Interpretation

Low apolipoprotein A-I level

A low Apo-A1 level indicates an increased risk of cardiovascular disease, especially in the presence of an elevated apolipoprotein B (Apo-B) level.[1, 2, 3, 4]

Other factors that are associated with low Apo A1 level include the following:

High apolipoprotein A-I level

High Apo-A1 levels are associated with the following:

  • Pregnancy
  • Alcohol use
  • Spring and summer seasons[5]
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Collection and Panels

Patient instructions: Overnight fasting (12-14 hours)

Collection tube: Lavender top (EDTA)

Unacceptable conditions: Hemolyzed specimens

Specimen preparation: Separate serum from cells as soon as possible or within 2 hours of collection and transfer to 1-mL serum transport tube

Storage/transport temperature: Refrigerated

Stability refrigerated: 8 days unfrozen; 3 months frozen

Panels: None

CPT Code: 82172

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Background

Description

Apolipoprotein A-I (Apo-A1) is a structural and functional protein that constitutes approximately 70% of the protein in HDL.

Apo-A1 is produced in the liver and intestines and activates lecithin-cholesterol acyltransferase (LCAT) in the peripheral tissues, which transforms free cholesterol to cholesterol ester and facilitates its transportation to the liver, were it is degraded.

Indications/Applications

Because it is not clear whether Apo-A1 is an independent predictor of cardiovascular disease, it may be useful to be measured in conjunction with Apo-B to assess the Apo-B/Apo-A1 ratio.

A higher ratio means an increased likelihood of cholesterol deposition in arteries, leading to atherosclerosis and a higher risk of cardiovascular disease.

Apo-A1 is one of many serum markers used in the fibroTest, a noninvasive assessment of the liver that was validated in many liver disease, including hepatitis C, hepatitis B, nonalcoholic fatty liver disease, and alcoholic liver disease.

Considerations

Serum Apo-A1 is not considered a routine test for cardiovascular disease risk assessment.

Overnight fasting might not be necessary to evaluate apo-A1, but most of the laboratories still commend it.

Apo-A1 Milano is a naturally occurring mutant of Apo-A1 associated with a very low HDL level but apparent longevity and much less atherosclerosis than expected for their HDL-C levels.[6]

A defect in the Apo-A1 gene (APOA1) can cause HDL deficiency and systemic nonneuropathic amyloidosis.

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Contributor Information and Disclosures
Author

Georges Elhomsy, MD Fellow in Endocrinology, St Louis University School of Medicine

Georges Elhomsy, MD is a member of the following medical societies: American Association of Clinical Endocrinologists, American Thyroid Association, Endocrine Society

Disclosure: Nothing to disclose.

Coauthor(s)

George T Griffing, MD Professor Emeritus of Medicine, St Louis University School of Medicine

George T Griffing, MD is a member of the following medical societies: American Association for the Advancement of Science, International Society for Clinical Densitometry, Southern Society for Clinical Investigation, American College of Medical Practice Executives, American Association for Physician Leadership, American College of Physicians, American Diabetes Association, American Federation for Medical Research, American Heart Association, Central Society for Clinical and Translational Research, Endocrine Society

Disclosure: Nothing to disclose.

Chief Editor

Eric B Staros, MD Associate Professor of Pathology, St Louis University School of Medicine; Director of Clinical Laboratories, Director of Cytopathology, Department of Pathology, St Louis University Hospital

Eric B Staros, MD is a member of the following medical societies: American Medical Association, American Society for Clinical Pathology, College of American Pathologists, Association for Molecular Pathology

Disclosure: Nothing to disclose.

References
  1. Teixeira PC, Ducret A, Ferber P, Gaertner H, Hartley O, Pagano S, et al. Definition of human apolipoprotein A-I epitopes recognized by autoantibodies present in patients with cardiovascular diseases. J Biol Chem. 2014 Aug 28. [Medline].

  2. Cochran BJ, Bisoendial RJ, Hou L, Glaros E, Rossy J, Thomas SR, et al. Apolipoprotein A-I Increases Insulin Secretion and Production From Pancreatic ß-Cells via a G-Protein-cAMP-PKA-FoxO1-Dependent Mechanism. Arterioscler Thromb Vasc Biol. 2014 Aug 21. [Medline].

  3. Li XL, Li JJ, Guo YL, Zhu CG, Qing P, Wu NQ, et al. The Ratio of High-Density Lipoprotein Cholesterol to Apolipoprotein A-I Predicts Myocardial Injury Following Elective Percutaneous Coronary Intervention. Clin Cardiol. 2014 Aug 11. [Medline].

  4. Rogacev KS, Zawada AM, Emrich I, Seiler S, Böhm M, Fliser D, et al. Lower Apo A-I and Lower HDL-C Levels Are Associated With Higher Intermediate CD14++CD16+ Monocyte Counts That Predict Cardiovascular Events in Chronic Kidney Disease. Arterioscler Thromb Vasc Biol. 2014 Sep. 34(9):2120-7. [Medline].

  5. Mustad V, Derr J, Reddy CC, Pearson TA, Kris-Etherton PM. Seasonal variation in parameters related to coronary heart disease risk in young men. Atherosclerosis. 1996 Sep 27. 126(1):117-29. [Medline].

  6. Nissen SE, Tsunoda T, Tuzcu EM, Schoenhagen P, Cooper CJ, Yasin M. Effect of recombinant ApoA-I Milano on coronary atherosclerosis in patients with acute coronary syndromes: a randomized controlled trial. JAMA. 2003 Nov 5. 290(17):2292-300. [Medline].

  7. Chiang SL, Ou TT, Wu YJ, Tu HP, Lu CY, Huang CM, et al. Increased level of MSU crystal-bound protein apolipoprotein A-I in acute gouty arthritis. Scand J Rheumatol. 2014 Sep 2. 1-5. [Medline].

  8. Contois J, McNamara JR, Lammi-Keefe C, Wilson PW, Massov T, Schaefer EJ. Reference intervals for plasma apolipoprotein A-1 determined with a standardized commercial immunoturbidimetric assay: results from the Framingham Offspring Study. Clin Chem. 1996 Apr. 42(4):507-14. [Medline].

  9. Davidson MH. Apolipoprotein measurements: is more widespread use clinically indicated?. Clin Cardiol. 2009 Sep. 32(9):482-6. [Medline].

  10. Evans K, Laker MF. Intra-individual factors affecting lipid, lipoprotein and apolipoprotein measurement: a review. Ann Clin Biochem. 1995 May. 32 ( Pt 3):261-80. [Medline].

  11. Gonzalez AI, Brites F, Elbert A, Gomez-Rosso L, Berg G, Wikinski R. [Relation between paraoxonase activity, other HDL components and inflammatory state in hemodialyzed patients]. Medicina (B Aires). 2010. 70(6):508-12. [Medline].

  12. http://www.mayomedicallaboratories.com/test-catalog/print.php?unit_code=80309. Feb 2012.

  13. Myers GL, Christenson RH, Cushman M, Ballantyne CM, Cooper GR. National Academy of Clinical Biochemistry Laboratory Medicine Practice guidelines: emerging biomarkers for primary prevention of cardiovascular disease. Clin Chem. 2009 Feb. 55(2):378-84. [Medline].

  14. Zannis VI, Chroni A, Krieger M. Role of apoA-I, ABCA1, LCAT, and SR-BI in the biogenesis of HDL. J Mol Med (Berl). 2006 Apr. 84(4):276-94. [Medline].

  15. Zhu W, Liu M, Wang GC, Peng B, Yan Y, Che JP, et al. Fibrinogen alpha chain precursor and apolipoprotein a-I in urine as biomarkers for noninvasive diagnosis of calcium oxalate nephrolithiasis: a proteomics study. Biomed Res Int. 2014. 2014:415651. [Medline]. [Full Text].

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