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:
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Men: Greater than 120 mg/dL (1.2 g/L)
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Women: Greater than 140 mg/dL (1.4 g/L)
levels decrease with age.
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:
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Chronic liver disease
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Smoking
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High triglyceride level
High apolipoprotein A-I level
High Apo-A1 levels are associated with the following:
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Pregnancy
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Alcohol use
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Spring and summer seasons [5]
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
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.
