sdLDL is a biochemical subclass of low-density lipoprotein defined by particle size and density rather than a separate molecule. Lipoproteins like LDL transport cholesterol and triglycerides in blood; sdLDL represents the smaller, more compact end of the LDL particle distribution. Clinically, sdLDL was characterized as a distinct, atherogenic fraction in epidemiologic and mechanistic studies beginning in the late 20th century, when particle-size analyses revealed links between small particles and vascular changes. Biologically, sdLDL particles have a higher protein-to-lipid ratio, greater susceptibility to oxidative modification, and a tendency to bind arterial proteoglycans and infiltrate the vessel wall. These properties can influence how lipids interact with the arterial lining and inflammatory processes, making sdLDL a useful marker for assessing lipid behavior beyond total LDL concentration.

Higher proportions or concentrations of sdLDL are associated with lipid patterns such as elevated triglycerides, low HDL cholesterol, insulin resistance, and certain metabolic states; these patterns are linked to greater particle retention and oxidative vulnerability in arteries. Conversely, lower sdLDL levels generally reflect a lipid profile dominated by larger, more buoyant LDL particles, which are less prone to those specific behaviors. Interpretation requires the full Cardio Zoomer context—sdLDL adds detail about particle quality and is most informative when considered alongside ApoB, total LDL particle measures, triglycerides, inflammatory markers, and metabolic indicators.

Cardio Zoomer includes sdLDL to refine assessment of lipid quality and particle behavior, not just quantity. sdLDL helps distinguish whether lipid-related vascular stress arises from particle composition, metabolic drivers, or combined pathways, supporting a clearer, more personalized risk map for clinicians.