ApoB

ApoB is present on several particle classes, including very-low-density, intermediate-density, low-density, and lipoprotein(a) particles. Because each of these particles carries one ApoB molecule, a blood concentration can serve as an estimate of their combined particle number rather than the amount of cholesterol inside them.

This differs from LDL cholesterol, which estimates cholesterol mass within a subset of particles. Particle cholesterol content varies, so the two measurements can be discordant. ApoB also does not identify how many particles are specifically lipoprotein(a), and it does not replace the additional context provided by triglycerides, cholesterol fractions, and other measurements.

Laboratory units and reference or decision thresholds should stay attached to the report. Fasting status, method, biological variation, and the clinical question can matter. ApoB is a risk-related biomarker, not an image of arterial plaque and not a diagnosis by itself.

The protein name also appears in forms such as ApoB-100 and ApoB-48. Circulating assays used for cardiovascular context chiefly reflect ApoB-100-containing particles, while intestinally derived particles involve ApoB-48. A laboratory's stated analyte and method define the reported concentration.

ApoB particle concentration and particle size describe different features. Two samples can contain a similar cholesterol mass distributed among different numbers of particles, which is why ApoB and cholesterol-based values may provide related yet nonidentical information.