Application of a modified precipitation method for the measurement of small dense LDL-cholesterol (sd-LDL-C) in a population in southern Brazil

BACKGROUND: In the study reported herein, we used the precipitation method employing heparin-Mg(2+), with slight modifications to avoid lipemia interference, to measure small dense-low density lipoprotein-cholesterol (sd-LDL-C) in Brazilian subjects with a high risk of developing cardiovascular diseases. METHODS: Lipemic samples were diluted with various solvents prior to precipitation with heparin-Mg(2+). Validation assays were performed with ultracentrifugation (n=100) and the reproducibility of sd-LDL-C measured in diluted serum (n=50). The applicability of this modification was evaluated by measuring sd-LDL-C in 434 southern Brazilian normolipidemic, dyslipidemic and type 2 diabetes mellitus (T2DM) individuals. RESULTS: Lipemic serum diluted with 100 mmol/L phosphate buffer pH 8.5 was effective for the quantification of sd-LDL-C, which was correlated with non-diluted serum (r=0.961; p 0.05). Subjects with dyslipidemias and T2DM had, respectively, 2.3 and 2.6-fold higher sd-LDL-C concentrations than normolipidemic individuals (p<0.05). The incidence of normolipidemic subjects with a high concentration of sd-LDL-C was only 2.2%. The sd-LDL-C was found to be enhanced by 8.3% every 10 years and young normolipidemic men had 24% higher sd-LDL-C than young women (p<0.05). Lipid-lowering therapy reduced sd-LDL-C by 26% (p<0.001). CONCLUSIONS: In this paper we described a simple and inexpensive approach to improving the measurement of sd-LDL-C in high-triglycerides serum. Furthermore, we showed that southern Brazil dyslipidemic and T2DM individuals have increased sd-LDL-C concentrations.