Apolipoprotein B

Apolipoprotein B (apoB) levels are used to evaluate the risk for cardiovascular disease. ^[1]

The reference range of apoB levels in adults is less than 130 mg/dL (1.3 g/L).

ApoB levels are higher in males than in females and tend to increase with age.

It has been suggested the range be adjusted according to the risk factor stratification, ^[2] similar to low-density lipoprotein cholesterol (LDL-C).

Table 1.  Treatment Goals for Total ApoB Relative to LDL-C Levels (Open Table in a new window)

 

Table 2. ADA/ACC Consensus Report Treatment Goals in Patients with Cardiometabolic Risk and Lipoprotein Abnormalities ^[3] (Open Table in a new window)

Elevated apolipoprotein B (apoB) levels indicate an increased risk of cardiovascular disease. ^{[4, 5, 6, 7]}

ApoB levels may be increased during pregnancy or coffee consumption, as well as during the fall and winter seasons.

Low apoB levels may indicate Bassen-Kornzweig syndrome (abetalipoproteinemia), a very rare genetic condition characterized by apolipoprotein B deficiency.

Other conditions that are associated with low apoB levels include the following:

• Liver cirrhosis

• Malnutrition

• Hyperthyroidism

Specimen type: Plasma EDTA

Patient instruction: 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 1 mL serum to transport tube

Storage/transport temperature: Refrigerated

Stability: Refrigerated 8 days; frozen 3 months

Panels: None

Description

Apolipoprotein B (apoB) is a structural protein that constitutes a major component of the very-low-density lipoprotein (VLDL), the intermediate-density lipoprotein (IDL), and the low-density lipoprotein (LDL). Each of these lipoprotein particles carries one apoB molecule; as a result, the total serum apoB level corresponds to the total number of VLDL, IDL, and LDL particles.

Because VLDL, IDL, and LDL are considered atherogenic, the apoB level should reflect the atherogenic potential of these lipoproteins.

Cardiovascular risk is associated more with the number and size of circulating atherogenic particles than with the concentration of cholesterol in these particles. ApoB is not equivalent to non-LDL-C, because the latter reflects the cholesterol content of all atherogenic lipoproteins rather than the total number of circulating atherogenic particles.

ApoB plays a central role in carrying cholesterol and triglycerides from the liver and gut to utilization and storage sites.

Indications/Applications

Incontestable data support the concept that apoB is a better tool to assess cardiovascular disease than LDL-C and non-HDL-C.

Furthermore, apoB seems to be a very important parameter in assessing cardiovascular risk in the setting of diabetes and metabolic syndrome, since patients with these conditions tend to have small, dense LDL particles with relatively normal LDL-C but high apoB levels.

In addition, several clinical trials have shown that apoB is a better marker for monitoring patients on statin therapy for residual risk than LDL-C. For example, a study by Johannesen et al indicated that in patients treated with statins, an association exists between high levels of apoB and non-HDL-C and greater residual risk of all-cause mortality and myocardial infarction. High LDL-C, however, was found to carry no such association. ^[8]

Finally, a Consensus Conference Report by the ADA/ACC has recommended the use of apoB level for risk assessment in persons at high risk for cardiometabolic disease.

Considerations

Familial hypercholesterolemia is a rare disease caused by a mutation in the apoB gene code. Patients with the homozygous mutation tend to develop cardiovascular disease in childhood.

Overnight fasting might not be necessary to evaluate apoB levels, but most laboratories recommend it.

Some evidence has shown that the capacity of the apoB/apoA-I ratio in assessing cardiovascular risk is strong and may be better than the use of apoB alone.

A prospective cohort study by Xiao et al indicated that as a risk factor, the apoB/apoA1 ratio is more strongly associated with abdominal aortic aneurysm (AAA) then with coronary heart disease (CHD), despite the relationship of both conditions to atherosclerosis. In addition, apoA1 was found to have a greater protective effect against AAA than CHD. ^[9]

A study by Perak et al indicated that in young people in the United States, there has been a favorable, downward trend in levels of apoB. The report, which involved 26,047 youths aged 6-19 years, found that between 2005-2006 and 2013-2014, the mean level of apoB in fasting adolescents fell from 70 mg/dL to 67 mg/dL. In addition, the investigators, who looked at lipid and apolipoprotein levels from 1999-2000 to 2015-2016, determined that by the end of the review period, ideal levels of all lipids and apoB were present in 46.8% of adolescents. ^[10]