Measurement of serum low density lipoprotein-cholesterol in patients with hypertriglycemia

Low density lipoprotein-cholesterol (LDL-c) concentration measured by a homogeneous enzymatic assay was reported to correlate well with the modified beta-quantification assay, especially in samples with high triglyceride (TG) concentration. In this study, we evaluated a homogeneous enzymatic assay, Cholestest(R)-LDL assay system, in hypertriglycemic patient samples, and found that 56% (9/16) of serum samples with intermediate TG concentrations (2.27-4.52 mmol/L) showed more than 10% discrepancy with concentration by the modified beta-quantification assay. Such serum samples originated from patients with hyperglycemia of type II a (three cases), type II b (two cases), type III (one case), and type IV (six cases). Differential staining of cholesterol and triglyceride after agarose gel electrophoresis revealed that these serum samples contained significant amounts of intermediate fractions between pre-beta- and beta-lipoproteins. Since lipoprotein (a), which migrates between pre-beta- and beta-lipoproteins, is not correlated with the discrepancy, we believe the intermediate fraction consists of intermediate density lipoprotein (IDL) and a chylomicron remnant. A part of IDL and chylomicron remnant, which contain a significant amount of triglyceride, might be measured as LDL-c by the homogeneous enzymatic assay, but not by the modified beta-quantification assay.