Do low HDL cholesterol and high LDL particle number increase ASCVD risk?

Atherosclerotic cardiovascular disease (ASCVD) risk is determined not just by the total amount of cholesterol in the blood, but more critically by the distribution and number of the particles that carry it. Decades of research have established that the concentration of protective high-density lipoproteins (HDL) and the absolute count of potentially harmful low-density lipoproteins (LDL) are primary indicators of long-term arterial health.

Clinical effectiveness and risk associations

Extensive prospective cohort studies consistently demonstrate that low HDL cholesterol (HDL-C) and high LDL particle numbers (LDL-P) are independent predictors of cardiovascular events.

• Low HDL-C: Data from large-scale studies involving over 5 million individuals show that low baseline HDL-C (typically ≤41.8 mg/dL) significantly increases the risk of myocardial infarction. Long-term trajectories suggest that individuals with sustained low HDL-C levels (<40 mg/dL) may face a 3-fold higher risk of ASCVD compared to those with high levels.
• LDL-P Superiority: While traditional LDL-C measures the total mass of cholesterol, LDL-P measures the number of individual particles. In cases where these metrics are discordant—common in metabolic syndrome—the particle number is a more accurate predictor of risk. High LDL-P can increase the risk of coronary events by up to 50% even when standard LDL-C levels appear normal.

Mechanistic explanations

The risk associated with these biomarkers is rooted in the fundamental biology of how cholesterol interacts with the arterial wall.

• Particle Burden and Entrapment: Atherosclerosis is initiated by the retention of Apolipoprotein B (ApoB)-containing particles, such as LDL, within the subendothelial space. Because each LDL particle carries one ApoB molecule, LDL-P is a direct measure of the particle burden. A higher number of particles increases the statistical probability that they will penetrate and become trapped in the arterial intima, where they oxidize and trigger plaque formation.
• Reverse Cholesterol Transport: HDL facilitates "reverse cholesterol transport," a process where it removes excess cholesterol from macrophages in the arterial wall. Low levels of HDL-C often reflect a reduced "cholesterol efflux capacity" (CEC). When CEC is impaired, the body’s ability to clear cholesterol from the arteries is diminished, accelerating subclinical atherosclerosis.

Bottom line

Low HDL-C and elevated LDL-P are both strongly associated with increased ASCVD risk. While LDL-P more accurately reflects the total burden of atherogenic particles entering the arterial wall, low HDL-C serves as a critical marker for impaired cholesterol clearance and overall metabolic dysfunction.