Background :Most of clinical laboratories currently estimate low-density lipoprotein cholesterol (LDL-C) using the Friedewald equation (FLDL-C) , which requires fasting specimens and is inaccurate with increasing triglyceride (TG) levels. The author evaluated a new assay which directly measures LDL-C (DLDL-C) using the direct LDL immunoseparation reagent and subsequent measurement of cholesterol by conventional method. Method :Direct LDL-cholesterol assay (Sigma Diagnostics, St. Louis, MO) was analyzed in 110 fresh serum samples from fasting patients for physical examination at Ewha Womans University Tongdaemun Hospital. In FLDL-C, total cholesterol and TG were measured by enzymatic methods and HDL-C by direct method. Lp(a), apo-A and apomB were measured by nephelometry (Array 360, Beckman, USA). The paired t-test, Pearson product-moment correlation coefficients and linear regression were calculated by Microsoft Excel. Withinrun precision and between-run precision were determined by two level reagent control sera containing normal and high concentration. Result :Precision studies were provided within and between-run CVs in the range of 2.9-5.8% and 6.5-12.1%, respectively. On the comparison of the bias between FLDL-C and DLDL-C, there was no significant difference between the two methods in 0.37-6.48 g/L TG and the same in less than 4.0 and 2.0 g/L TG. But the results of DLDL-C were higher than FLDL-C (P Conclusion :There was a high positive correlation between DLDL-C and FLDL-C below TG 4.0 g/L and direct determination is necessary above 2.0 g/L of TG and will require proper calibrators in measuring the DLDL-C.

Keywords: Direct LDL-C assay, Friedewald equation, Low-density lipoprotein cholesterol, Immunoseparation method