In most of the studies using these methods, LDL particles are classified into 3 or 4 subclasses, including large (LDL I), intermediate (LDL II), small (LDL III), and, in some studies, very small (LDL IV) LDLs [3, 18]. LDL III and LDL IV (when discerned) are referred to as sdLDL.

Introduction. LDL cholesterol, or low-density lipoprotein cholesterol, is a fat that circulates in the blood, moving cholesterol around the body to where it is needed for cell repair and depositing it inside of artery walls.

LDL contain 22% apoB-100, 22% phospholipids, 8% cholesterol, 42% cholesteryl esters, and 6% triglycerides (wt/wt). Structural studies (4–14) of LDL indicate a range of particle sizes (180–250 Å). This variation has been attributed to the differences in lipid content of LDL (5–8).

The LDL Principle has recently been invoked to describe the observation that lowering the LDL cholesterol (by whatever means) results in a lowering of atherosclerotic cardiovascular events.