Evaluation of a new homogenous method for detection of small dense LDL cholesterol: comparison with the LDL cholesterol profile obtained by density gradient ultracentrifugation.

Background: Small, dense LDL (sdLDL) are highly atherogenic, and evidence indicates that sdLDL are useful predictors of cardiovascular disease. We evaluated a homogeneous method for the quantitative determination of sdLDL cholesterol (sdLDL-C) and compared it to the LDL-cholesterol profile obtained by density gradient ultracentrifugation (DGUC).

Methods: sdLDL-C was measured in plasma and in lipoprotein fractions obtained by DGUC using the sdLDL-EX "Seiken" kit.

Results: sdLDL-C was only present in dense or intermediate LDL fractions obtained by DGUC. Plasma sdLDL-C levels were inversely corelated to the LDL relative floatation rate. The proportion of LDL-C that is sdLDL-C increases as a function of LDL density from a median of 19% for very buoyant LDL to 91% for very dense LDL particles. Plasma sdLDL-C level was significantly correlated with plasma triglyceride (TG) (n=840, r(s)=0.710, p<0.001). Among subjects with plasma TG>150 mg/dl, 75% had sdLDL-C>30 mg/dl, whereas among those with TG ≤ 150 mg/dl, only 17% had sdLDL-C>30 mg/dl.

Conclusions: This precise and fully automated method for measuring plasma levels of sdLDL-C will allow the analysis of large number of samples in routine laboratories which will facilitate the evaluation of the clinical usefulness of sdLDL as a risk factor for CHD.