LowDensityLipoprotein

Low-density lipoprotein (LDL) is one of the major classes of lipoproteins that transport lipids in the bloodstream. LDL particles are relatively rich in cholesterol and are commonly referred to as "bad cholesterol" because elevated levels are associated with a higher risk of atherosclerotic cardiovascular disease. LDL is formed from very-low-density lipoprotein (VLDL) after triglyceride removal by lipoprotein lipase, primarily in the circulation and in the liver.

Structure and function: LDL particles consist of a cholesterol-rich core surrounded by a shell of phospholipids and cholesteryl esters, with a single molecule of apolipoprotein B-100 on the surface. The main physiological role of LDL is to deliver cholesterol to cells via LDL receptor–mediated endocytosis. Cells use cholesterol for membrane synthesis and steroid production; excessive uptake can contribute to cholesterol accumulation in arterial walls and plaque formation.

Clinical significance: LDL cholesterol measurement is part of standard lipid panels. High LDL cholesterol is a well-established risk factor for atherosclerotic cardiovascular disease (ASCVD). Guidelines set target LDL-C levels based on overall cardiovascular risk, with stricter goals for high-risk individuals. In the United States, results are typically reported in mg/dL, while many other regions use mmol/L.

Genetics and treatment: Familial hypercholesterolemia causes markedly elevated LDL-C due to mutations affecting LDL receptors or apoB, increasing ASCVD risk. Management includes lifestyle changes and lipid-lowering medications. Statins are first-line therapy; ezetimibe, PCSK9 inhibitors, and bempedoic acid serve as add-ons or alternatives. LDL particle size can vary; small dense LDL particles are considered more atherogenic, though total LDL-C remains the primary risk marker used in practice.