Evaluation of two different homogeneous assays for LDL-cholesterol in lipoprotein-X-positive serum.
BACKGROUND
The purpose of this study was to evaluate the performance of two homogeneous assays for LDL-cholesterol (LDL-C), a polyethylene/cyclodextrin (PC) assay and a detergent (D) assay, which are based on different principles, in cholestatic serum.


METHODS
We compared serum LDL-C concentrations determined by the two assays for healthy normolipidemic subjects (n = 42) and cholestatic patients (n = 51). LDL-C concentrations obtained with the homogeneous assays were also compared with those obtained by HPLC for patients' sera. In the interference study, conjugated bile acids were added to normal serum, and their effects on the two assays were examined. The effects of lipoprotein-X (LP-X), intermediate-density lipoprotein (IDL), and apolipoprotein (apo) E-rich HDL on the LDL-C assays were also investigated by adding these lipoproteins to normal serum.


RESULTS
The LDL-C concentrations obtained with the D assay were higher than those obtained with the PC assay in the serum with high LP-X. The bias for LDL-C vs LP-X in cholestatic serum correlated with LP-X concentration (r = 0.582; P: <0.0001; n = 51). In the interference study, no effect of bile acids on the LDL-C assays was observed. However, the D assay measured 51.0% of the cholesterol in LP-X, whereas no reactivity was observed for LP-X in the PC assay. In addition, the D assay and the PC assay measured IDL-cholesterol at 31.2% and 52.4%, respectively, and measured apo E-rich HDL-C at 7.6% and 17.8%, respectively.


CONCLUSIONS
Although both homogeneous LDL-C assays are suitable for most cases, the present study showed that each homogeneous assay has a different limitation for cholestatic serum with gross alterations in lipoproteins.
Fei
H
H
Department of Laboratory Medicine, Gifu University School of Medicine, 40 Tsukasa-machi, Gifu 500-8705, Japan.
Maeda
S
S
Kirii
H
H
Fujigaki
S
S
Maekawa
N
N
Fujii
H
H
Wada
H
H
Saito
K
K
Seishima
M
M
D000328:Adult; D000368:Aged; D001057:Apolipoproteins E / Q000097:blood; D002779:Cholestasis / Q000097:blood; D008078:Cholesterol, LDL / Q000097:blood*; D002851:Chromatography, High Pressure Liquid; D003505:Cyclodextrins; D003902:Detergents; D006801:Humans; D008073:Lipoprotein-X / Q000097:blood*; D008075:Lipoproteins, HDL / Q000097:blood; D008875:Middle Aged; D020959:Polyethylene
D001057:Apolipoproteins E; D008078:Cholesterol, LDL; D003505:Cyclodextrins; D003902:Detergents; D008073:Lipoprotein-X; D008075:Lipoproteins, HDL; D020959:Polyethylene