Apolipoprotein A-I 

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