Apolipoprotein B

Order Code

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4003

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 samples

Overview

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Apolipoprotein B (Apo B) is one of several apolipoproteins which structurally bind and help solubilize circulating lipoprotein, as well as function as cofactors for enzymes and ligands for receptors (Mahley 1984; Rosenson 2019). Apo B plays a central role in carrying cholesterol and triglycerides from the liver and intestine to utilization and storage sites (Elhomsy 2014).

The two forms of Apo B produced from the APOB gene by posttranscriptional editing are Apo B-100 and Apo B-48.

• Apo B-100 is required for VLDL production in the liver and also functions as the ligand for LDL-receptor-mediated endocytosis of LDL particles, promoting cholesterol uptake into cells.
• Exactly one Apo B-100 is present in each LDL cholesterol particle, where it represents 95% of the total protein present (Bancells 2010). High levels of Apo B-100 are associated with increased risk for cardiovascular diseases (CVD) (Whitfield 2004).
• Apo B-48 is required for chylomicron production in the small intestine and is not recognized by the LDL receptor (Feingold 2018).

The Apo B test is specific for Apo B-100.
Apo B-100 is considered one of the nontraditional markers of CVD and is not currently recommended for routine CVD assessment by most major US guidelines. Apo B-100 levels may be appropriate in certain populations at high risk for CVD, as well as to help diagnose genetic disorders that cause overproduction or underproduction of Apo B (Elhomsy 2014; Greenland 2010).

Clinical Significance

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• Not currently recommended for routine CVD risk assessment in asymptomatic adults by the 2010 American College of Cardiology Foundation/American Heart Association guidelines (Greenland 2010).
• Useful for individuals with strong personal or family history of CVD and/or high cholesterol and triglycerides, especially in the presence of premature CVD.
• Monitor effectiveness of intervention (dietary changes, exercise, medication).
• Diagnose rare inherited or acquired conditions of apolipoprotein B that can cause hypercholesterolemia (overproduction of Apo B) or hypobetalipoproteinemia (underproduction of Apo B).

Additional Information

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The two forms of Apo B (Apo B-100, Apo B-48) are encoded by a single gene (APOB) and a single, very long mRNA.

• Apo B-48 is identical to the amino-terminal 48% of Apo B-100 and is produced by the small intestine, whereas full-length Apo B-100 is produced in the liver.

Mutations in APOB cause diseases affecting plasma cholesterol and Apo B levels:

• Familial defective APOB-100 (FDB): an autosomal dominant mutation that results in a conformational change in the apolipoprotein B-LDL complex preventing its binding to the LDL receptor. This slows clearance of LDL from blood, resulting in accumulation of LDL and increasing the risk of premature CVD (NLM 2012).
• Familial hypobetalipoproteinemia (FHBL): a rare genetic condition with abnormally low levels of Apo B-100 and consequent low LDL cholesterol levels and resistance to CVD (Whitfield 2004).
• Abetalipoproteinemia (MTTP gene mutation): an autosomal recessive disorder that interferes with normal absorption of fat and fat-soluble vitamins.
  • Heterozygotes: asymptomatic, normal lipid levels.
  • Homozygotes: absent LDL, resulting in fat malabsorption, progressive ataxia, acanthocytic red blood cells, and retinitis pigmentosa. Death usually occurs by age 30 (Lee 2014).

Apo B Form	Primary Source	Role
B-48	Intestine	Found on chylomicrons and required for assembly and secretion. Not considered a risk factor for CVD.
B-100	Liver	Found on VLDL, LDL, Lp(a). Required for assembly and secretion of VLDL. Ligand for LDL receptor.

Decrease Apo B	Increase Apo B
Malnutrition	Diabetes
Certain drugs (statins, estrogen, niacin, thyroxine)	Certain drugs (androgens, beta blockers, diuretics, progestins)
Hyperthyroidism	Hypothyroidism
Cirrhosis	Nephrotic Syndrome
Severe illness	Pregnancy
Weight loss	Familial defective APOB-1 (FDB)
Exercise	—
Familial hypobetalipoproteinemia (FHBL)	—
Abetalipoproteinemia (Bassen-Kornzweig syndrome)	—

Interpretative Information

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Refer to testing laboratory for lab-specific normal values and interpretation; values tend to be higher in males than females and increase with age.

Examples of ranges:

• Acceptable: <90 mg/dL
• Borderline high: 90–119 mg/dL
• High: ≥120 mg/dL

CVD Risk Category	Apo B-100 Level (mg/dL)	Comment
Low Risk	≤130	0–1 CVD risk factors
Moderate Risk	≤110	≥2 CVD risk factors
High Risk	≤90	≥3 CVD risk factors, but no diabetes mellitus (DM) or known CVD, or DM but no other major risk factors
Highest Risk	≤80	Known CVD or DM plus ≥1 additional major CVD risk factor(s)

Adapted from Brunzell 2008; Elhomsy 2014.

Limitations

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Rarely, samples with very high triglyceride levels may require retesting with a more dilute sample due to interference with assay.

References

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Diagnostic Role

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Controversy exists for the exact role of Apo B in CVD assessment and treatment.
Since there is exactly one molecule of Apo B-100 per atherogenic LDL particle, Apo B-100 is more representative of LDL concentration.
There is growing support for including Apo B measurement in routine lipid panels for assessing and monitoring patients at risk for cardiovascular disease (CVD).

As of 2018:

• ACC/AHA guidelines do not recommend Apo B for risk assessment in the general, asymptomatic population (Stone 2014).
• AACE/ACE guidelines do support Apo B-100 testing for high-risk groups such as obesity, diabetes, or dyslipidemia (Jellinger 2017).

Alias

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B-100 apolipoprotein

Test Setup Days

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Monday through Friday PM shift

CPT

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82172 LOINC: 1884-6

Reference Range

MALE:
AGE: 0-17 YEARS: <90 MG/DL
>=18 YEARS: 66-133 MG/DL
FEMALE:
AGE: 0-17 YEARS: <90 MG/DL
>=18 YEARS: 60-117 MG/DL

Unit Code	Unit Code Name	Analyte	Gender	Age	Reference Range	Units of Measure
4003	APOLIPO B	APOB	Not Specified	0 Y	60 – 133	mg/dL
4003	APOLIPO B	APOB	Not Specified	17 Y	< 90	mg/dL
4003	APOLIPO B	APOB	Not Specified	150 Y	60 – 133	mg/dL
4003	APOLIPO B	APOB	Male	0 Y	66 – 133	mg/dL
4003	APOLIPO B	APOB	Male	17 Y	< 90	mg/dL
4003	APOLIPO B	APOB	Male	150 Y	66 – 133	mg/dL
4003	APOLIPO B	APOB	Female	0 Y	60 – 117	mg/dL
4003	APOLIPO B	APOB	Female	17 Y	< 90	mg/dL
4003	APOLIPO B	APOB	Female	150 Y	60 – 117	mg/dL