Apolipoprotein B (ApoB): Clinical Overview
Introduction
Apolipoprotein B (ApoB) is a primary structural protein found in atherogenic lipoproteins — particularly low-density lipoprotein (LDL), very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and chylomicrons. Each atherogenic particle contains one ApoB molecule, making ApoB a direct measure of the number of circulating atherogenic particles.

This marker plays a vital role in evaluating the risk of cardiovascular diseases and provides more specific information than LDL cholesterol alone.

Types of ApoB
There are two isoforms of ApoB:

ApoB-100: Synthesized in the liver, found in LDL, VLDL, IDL — measured in blood tests.

ApoB-48: Synthesized in the intestine, found in chylomicrons — not typically measured in standard blood panels.

Function
ApoB is essential for the assembly and secretion of lipoproteins that transport cholesterol and triglycerides in the bloodstream.

It facilitates the uptake of lipoproteins by cells via LDL receptors.

ApoB-containing particles can penetrate arterial walls, contributing to plaque formation and atherosclerosis.

Sample Type
Serum: Blood is collected, allowed to clot, and centrifuged to obtain serum for analysis.

Clinical Importance
ApoB is a:
Direct marker of the number of atherogenic particles (LDL, VLDL, IDL).

Better predictor of cardiovascular events than LDL-C in many populations.

Key marker for patients with metabolic syndrome, diabetes, or discordant lipid profiles.

Reference Ranges
Optimal: <90 mg/dL

Borderline high: 90–109 mg/dL

High: ≥110 mg/dL

Interpretation may vary depending on individual risk factors and clinical context.

Why Measure ApoB?
More accurate than LDL-C: LDL cholesterol measures the amount of cholesterol in LDL particles, not the number of particles. ApoB measures the number of atherogenic particles directly.

Useful in patients with normal LDL-C but high cardiovascular risk.

Valuable in monitoring lipid-lowering therapy, especially in people with obesity, insulin resistance, or high triglycerides.

Testing Method
Typically measured via immunoassay techniques such as nephelometry or immunoturbidimetry.

Requires no special preparation; however, fasting may be recommended if part of a broader lipid profile test.

Clinical Conditions Associated with ApoB
Increased ApoB: Atherosclerosis, familial hypercholesterolemia, type 2 diabetes, metabolic syndrome, hypothyroidism

Decreased ApoB: Malnutrition, liver disease, abetalipoproteinemia

Comparison: ApoB vs LDL-C
Parameter ApoB LDL-C
What it measures Number of atherogenic particles Amount of cholesterol in LDL
Accuracy in risk High (especially in mixed dyslipidemia) Moderate
Affected by triglycerides No Yes

Conclusion
Apolipoprotein B is a powerful biomarker for identifying and managing cardiovascular risk. Measuring ApoB provides a more accurate representation of atherogenic particle burden than LDL-C alone and is particularly beneficial in individuals with complex lipid disorders. It is now increasingly used as part of a comprehensive lipid assessment in clinical practice.