Apolipoprotein A-1

Order Code

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4004

Preferred Specimen

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1 mL serum. Allow SST to clot in an upright position for at least 30 minutes, then centrifuge sample within 2 hours of collection. Refrigerate.

Container Type

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Serum separator tube

Alternate Specimen Requirements

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1 mL serum from a plain red top tube. Allow sample to clot in an upright position for at least 60 minutes, then centrifuge sample and transfer serum to a plastic transport tube within 2 hours of collection. Clearly label tube as serum from a plain red top tube. Refrigerate.

Minimum Volume

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• 0.5 mL serum

Transport Temperature

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Refrigerated

Expected Turnaround Time

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1–3 days

Specimen Stability

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4 days room temperature; 8 days refrigerated; 2 months frozen

Methodology

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Immunoturbidimetric standardized to WHO-IRP reference standard IFCC SP1-01

Rejection Criteria:

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• Thawed specimens

Overview

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Apolipoprotein A (Apo A) is one of several apolipoproteins which structurally bind and help solubilize circulating lipoproteins. It also regulates and controls lipoprotein metabolism by serving as cofactors for enzymes and ligands for receptors (Mahley 1984; Rosenson 2019a). Apo A exists in multiple forms (Apo A-I, Apo A-II, Apo A-IV, Apo A-V), of which Apo A-I is the primary protein associated with HDL cholesterol and at present is the best understood.

Apo A-I is produced in the liver and intestines and makes up 65% to 70% of the protein mass in HDL. Apo A-I is a key mediator in cholesterol cellular homeostasis and transport in the blood through its function as a cofactor for lecithin-cholesterol acyltransferase (LCAT), an enzyme that facilitates cholesterol transfer via HDL lipoproteins to the liver for degradation (Elhomsy 2014). In particular, Apo A-I aids in the removal of cholesterol from white blood cells within artery walls, slowing their conversion into foam cells and preventing further progression of atherosclerosis (Mangaraj 2016).

The concentration of Apo A-I tends to rise and fall with HDL levels. High levels of Apo A-I are considered protective, while deficiencies in Apo A-I correlate with an increased risk of developing cardiovascular disease (CVD). Apo A-I levels are not recommended for routine CVD risk assessment in asymptomatic adults per the 2010 American College of Cardiology Foundation/American Heart Association guidelines, although a role exists in evaluating CVD risk when HDL levels are low (Elhomsy 2014; Greenland 2010).

Clinical Significance

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• Not recommended for routine CVD risk assessment in asymptomatic adults (2010 American College of Cardiology Foundation/American Heart Association guidelines) (Greenland 2010).
• Strong personal or family history of abnormal lipid levels (e.g., low HDL levels), especially in the presence of premature CVD.
• Monitor effectiveness of intervention (dietary changes, exercise, medication).
• Diagnose rare inherited or acquired conditions that cause Apo A-I deficiencies, such as familial alpha-lipoprotein deficiency.

Additional Information

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Apolipoprotein A	Primary Source	Role
Apo A-I	Liver, Intestine	Structural protein for HDLActivates LCATFound in HDL, chylomicrons
Apo A-II	Liver	Structural protein for HDLActivates hepatic lipaseFound in HDL, chylomicrons
Apo A-IV	Intestine	Function unknownFound in HDL, chylomicrons
Apo A-V	Liver	Promotes LPL mediated TG lipolysisFound in HDL, chylomicrons, VLDL

Adapted from Feingold 2018

Factors Affecting Apo A-I Levels

Decrease Apo A-I	Increase Apo A-I
Obesity	Weight Loss
Diabetes Mellitus (poorly controlled)	Exercise
Chronic Kidney Disease	Pregnancy
Chronic Liver Disease	Certain drugs (e.g., statins, niacin, estrogens, carbamazepine, phenobarbital, ethanol)
Tobacco Use	Familial Hyperalphalipoproteinemia
Certain drugs (e.g., androgens, progestins, beta blockers, diuretics)	Familial cholesteryl ester transfer protein deficiency (CETP)
Familial Hypoalphalipoproteinemia	—

Adapted from Elhomsy 2014

Interpretative Information

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Refer to testing laboratory for lab-specific normal values and interpretation. Examples of ranges:

Apolipoprotein A-I (mg/dL)	Female Adults	Male Adults	Children/Adolescents
Low Risk	>140	>120	>120
Borderline/High Risk	123–140	109–120	—
High Risk	<123	<109	<115

Adapted from Elhomsy 2014; Mayo 2018

Limitations

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Apo A-I measurement alone has not been shown of benefit over current recommended cholesterol parameters (Harada 2014).

References

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Diagnostic Role

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Apolipoprotein A-I levels are not recommended for routine screening in patients of average risk for cardiovascular disease (CVD). Apo A-I levels may be appropriate, however, in the presence of a strong personal or family history of abnormal lipid levels, in particular low HDL levels, and/or premature CVD. Following intervention (dietary changes, exercise, medication), Apo A-I levels may be ordered to monitor effectiveness.

Alias

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A-1 apolipoprotein

Test Setup Days

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Monday through Friday PM shift

CPT

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82172 LOINC: 1869-7

Reference Range

MALE:
AGE: 0-17 YEARS: >120 MG/DL
>=18 YEARS: 104-202 MG/DL
FEMALE:
AGE: 0-17 YEARS: >120 MG/DL
>=18 YEARS: 108-225 MG/DL

UNIT CODE	UNIT CODE NAME	ANALYTE	GENDER	AGE	REFERENCE RANGE	UNITS OF MEASURE
4004	APOLIPO A-1	APOA	NOT SPECIFIED	0Y	104-225	MG/DL
4004	APOLIPO A-1	APOA	NOT SPECIFIED	17Y	>120	MG/DL
4004	APOLIPO A-1	APOA	NOT SPECIFIED	150Y	104-225	MG/DL
4004	APOLIPO A-1	APOA	MALE	0Y	104-202	MG/DL
4004	APOLIPO A-1	APOA	MALE	17Y	>120	MG/DL
4004	APOLIPO A-1	APOA	MALE	150Y	104-202	MG/DL
4004	APOLIPO A-1	APOA	FEMALE	0Y	108-225	MG/DL
4004	APOLIPO A-1	APOA	FEMALE	17Y	>120	MG/DL
4004	APOLIPO A-1	APOA	FEMALE	150Y	108-225	MG/DL