[New simple method for small, dense LDL: development of a new quantification method and clinical significance]

Small, dense LDL (S LDL) is regarded as a significant risk factor for coronary heart disease (CHD) and has also been reported its high appearance in type 2 diabetic patients. Although ultracentrifugation and electrophoresis based methods are currently used for the measurement of S LDL, such methods are either too laborious or expensive for clinical use. We have developed a simple method for quantification of S LDL. The new method consists of two steps; first to filter out large buoyant LDL and other apoB-containing lipoproteins by forming aggregates of these unintended lipoproteins with a heparin-manganese based reagent; and second to measure S LDL-cholesterol (S LDL-C) in the penetrate solution, the mixture of HDL and S LDL, on automated general chemistry analyzers. Comparison with the ultracentrifugation method yielded a correlation coefficient of 0.900 and an equation of y = 1.090x-1.8 (n = 146). Positive correlation was observed with total LDL-C level and also with triglyceride level (r = 0.782 and r = 0.526, respectively) while negative correlation was observed with LDL particle size (r = 0.658). As for the study with various types of hyperlipidemia sample, the highest level of S LDL-C was observed in combined hyperlipidemia patients. Patients with CHD had higher S LDL-C than control group (45.2 +/- 22.1 in the CHD vs. 36.7 +/- 16.9 in the control), however no difference was seen in total LDL-C level between the two groups (117.6 +/- 35.0 in the CHD vs. 115.7 +/- 30.1 in the control). Patients with type 2 diabetes also showed higher S LDL-C (54.0 +/- 22.7). S LDL-C/LDL-C ratios were also significantly higher in CHD patients and in type 2 diabetes patients than the control group (39.9 +/- 16.7 in the CHD, 37.6 +/- 13.0 in the type 2 diabetes and 31.0 +/- 9.9 in the control). Our findings suggest that this method can measure S LDL reliably with a simple procedure and that the analysis of S LDL-C can give a better index for the risk assessment of CHD than total LDL-C.