LDL (low-density lipoprotein) cholesterol is the primary carrier of cholesterol from the liver to peripheral tissues. Often called 'bad' cholesterol, LDL particles — particularly when oxidised — can penetrate the arterial wall and trigger the inflammatory cascade that leads to atherosclerotic plaque formation, arterial narrowing, and ultimately heart attack and stroke.

LDL cholesterol is the primary treatment target in cardiovascular risk management. Australian guidelines recommend LDL below 2.0 mmol/L for high-risk individuals and below 1.8 mmol/L for those with established cardiovascular disease. However, LDL alone does not capture the full risk — particle number (ApoB) and particle size (subfraction testing) provide more complete risk stratification, particularly when LDL appears borderline.