Small dense low-density lipoprotein: Analytical review

The causal relationship between low-density lipoprotein (LDL) and atherosclerotic cardiovascular disease (CVD) has been firmly substantiated. LDL consists of a heterogeneous group of particles with different physicochemical and metabolic properties. Among them, small dense LDL (sdLDL) particles are considered an emerging CVD risk factor and a promising CVD risk biomarker. This paper reviews published analytical and calculation-based methods for sdLDL determination in plasma, present their principles, strengths, and weaknesses, and examine the challenges arising from method comparison.

A literature survey was conducted using the PubMed database. Subject headings and keywords facilitated the search strategy. Titles and abstracts were initially assessed, and the full-text article of the pre-selected ones was reviewed.

A range of methods is currently available for the analysis of LDL subfractions and the measurement of sdLDL particle size, number, and cholesterol concentration. Ultracentrifugation (UC), vertical auto profile, gradient gel electrophoresis (GGE), nuclear magnetic resonance (NMR) spectroscopy, high-performance liquid chromatography, ion mobility analysis, and a homogeneous assay are the most prevalent. To date, there is no "gold standard". UC and GGE are the most established techniques, albeit significantly sophisticated. NMR and the homogeneous assay are options with potential clinical use as they yield results rapidly and can be high-throughput. None of the proposed equations for the calculated sdLDL determination has been sufficiently validated to serve as a clinical tool.

Many analytical procedures have been developed for the study of sdLDL particles. Their use remains largely restricted to research laboratories since their analytical and clinical performance, along with the clinical- and cost-effectiveness of sdLDL determination have not been fully established.