J Clin Pathol Qual Control.  1999 Jun;21(1):159-165.

Direct Determination of Low-Density Lipoprotein Cholesterol using Homogeneous Method

• Lee MK
• Lee DS
• Park AJ

Abstract

BACKGROUND: Most clinical laboratories use the Friedewald equation for estimating low-density lipoprotein cholesterol (FLDL-C). However, this equation is invalid when fasting triglyceride (TG) levels are >400 mg/dL. These limitation creates the need for direct low-density lipoprotein cholesterol (LDL-C) assay. We evaluated a new homogeneous assay which directly measures LDL-C (DLDL-C) and established its reference values.
METHODS
DLDL-C (Daiichi Pure Chemicals Co., Japan) and FLDL-C were analyzed in 238 fresh samples from 40 patients and 198 healthy subjects. LDL-C were also measured by precipitation methods (PLDL-C) in some cases. Within-and between-run precision were determined by two levels of reagent control sera. The paired t-test, Pearson correlation coefficients and linear regression and Bland-Altman plots were calculated.
RESULTS
Within- and between-run precision showed 2.1%-2.3% and 2.4%-2.6%, respectively. In comparison with DLDL-C and FLDL-C, there was significant difference (P<0.001) regardless of TG levels. In less than 400 mg/dL TG (n=221), the correlation coefficient and regression equation between two methods were 0.915 and Y (DLDL-C) = 0.788Z (FLDL-C) + 39.5, but the Bland-Altman plots display considerable lack of agreement between methods. Among the tree methods of FLDL-C, PLDL-C and DLDL-C, there were significant difference (P<0.001). In healthy subjects, DLDL-C levels showed 127.6+/-30.3 mg/dL (mean+/-S.D.) and reference range (95% confidence interval) was 68.2-187.0 mg/dL.
CONCLUSIONS
Although further researches are required to confirm about the effects the various interfering factors to DLDL-C, the direct LDL-C assay may be suitable for routine use in the clinical laboratories.

MeSH Terms

Cholesterol*
Fasting
Humans
Linear Models
Lipoproteins*
Reference Values
Triglycerides
Cholesterol
Lipoproteins