**Apolipoprotein B (ApoB)** is the primary structural protein found in all atherogenic lipoproteins, including low-density lipoprotein (LDL), very low-density lipoprotein (VLDL), and intermediate-density lipoprotein (IDL). Synthesized in the liver and intestine, each atherogenic particle carries exactly one ApoB molecule, making its measurement a direct representation of total circulating atherogenic particle count. ApoB plays a critical role in lipid metabolism by facilitating the transport of cholesterol and triglycerides to peripheral tissues. Because elevated ApoB levels directly contribute to arterial plaque accumulation, measuring ApoB provides a highly precise clinical assessment for evaluating cardiovascular disease risk alongside standard lipid panels.