Evaluation of a Homogeneous Assay for Measuring LDL-cholesterol in Hyperlipidemic Serum Specimens

Abstract

Homogeneous assay reagents for the determination of low-density lipoprotein cholesterol (LDL-C) have been available from several manufacturers. However, there has been considerable controversy due to uncertainty regarding their reactivity with intermediate-density lipoprotein (IDL), which is detected at an especially high frequency in patients with type III hyperlipemia. In this study, we examined the reactivity of a homogeneous assay, Cholestest LDL (R) (CT-LDL), with hyperlipemic sera that were classified according to the WHO system. Sera from 6 normolipidemic and 22 hyperlipidemic patients classified according to the WHO system were used for this study. All serum specimens were fractionated by the ultracentrifugation method of Hatch and Lees, and subjected to lipid and protein measurements. The percent bias of values measured by CT-LDL relative to those determined by the ultracentrifugation method was calculated and compared to the lipid/protein ratios of each lipoprotein fraction. Consequently, the coefficient of correlation between the bias and the Triglyceride/Total cholesterol (TG/TC) ratio in the IDL fraction was 0.742. There were also correlations with the TG/TC ratio and the apo-lipoprotein B/Total Cholesterol ratio in the LDL fraction and in the LDL+IDL fraction, respectively. Further testing will be required in order to know more about the clinical condition of hyperlipidemic patients, since CT-LDL may react differently with some beta lipoproteins having a diverse lipid/protein composition compared to those in normolipidemic specimens.