LDL

Low-density lipoprotein (LDL) is a lipoprotein particle that transports cholesterol and other lipids through the bloodstream. LDL particles are formed from very low-density lipoprotein (VLDL) after triglyceride removal. Each particle contains a core of cholesterol esters and triglycerides surrounded by a phospholipid surface and a single molecule of apolipoprotein B-100 (ApoB-100), which enables receptor recognition.

LDL serves to deliver cholesterol to cells throughout the body by binding to LDL receptors on cell surfaces, particularly in the liver. The liver clears LDL from circulation via receptor-mediated endocytosis. Plasma levels of LDL-cholesterol (LDL-C) reflect a balance between hepatic production and peripheral clearance. Genetic factors, diet, and certain medications influence this balance. PCSK9 modulates receptor recycling and can raise LDL-C when activity is high.

In epidemiology and pathophysiology, elevated LDL-C is a major risk factor for atherosclerotic cardiovascular disease. Oxidized LDL and small dense LDL particles are thought to be more atherogenic, promoting endothelial dysfunction, inflammation, and plaque formation in arteries.

LDL-C is typically reported in milligrams per deciliter (mg/dL). When triglycerides are below 400 mg/dL, LDL-C is often estimated by the Friedewald equation: LDL-C ≈ total cholesterol − HDL-C − (triglycerides/5). Direct measurement can be used when triglycerides are high or in specific clinical contexts. Reference values are commonly described as: <100 mg/dL optimal, 100–129 near/above optimal, 130–159 borderline high, 160–189 high, and ≥190 mg/dL very high.

Management focuses on lowering LDL-C through lifestyle changes and medications. Diets emphasizing reduced saturated fat and cholesterol, regular physical activity, weight management, and smoking cessation are recommended, along with pharmacologic therapies such as statins, ezetimibe, and, when indicated, PCSK9 inhibitors or other agents.