Measurement of serum remnant-like lipoprotein particle-triglyceride (RLP-TG) and RLP-TG/total TG ratio using highly sensitive triglyceride assay reagent

Serum concentration of remnant-like lipoprotein particles (RLP) have been measured by cholesterol as RLP-C for clinical diagnostic purpose. However, the measurement of TG in RLP and the ratio of RLP-TG/total TG has not been well established. Highly sensitive triglyceride assay reagent (TG-EX) was used for RLP-TG assay and compared with the previously used TG reagent (Determiner LTGII). Sera in health check-up populations, cardiovascular disease, diabetes and oral fat load cases were used for the evaluation of the new RLP-TG assay. Serum TC, TG, HDL-C, LDL-C and RLP-C concentrations were also determined in above cases. The detection limit of new RLP-TG using TG-EX was 2.0 mg/dl. The within-run imprecision (n = 10) was CV = 3.0% (RLP-TG: 4.1 mg ± 0.7 mg/dl), CV = 1.4% (RLP-TG: 42.0 ± 0.6 mg/dl) and CV = 0.5% (RLP-TG: 100.6 ± 0.6 mg/dl). Cut-off value (75 percentile) of RLP-TG determined in the fasting Japanese population was 13.1 mg/dl in men and 9.9 mg/dl in women. In patients with metabolic syndrome, cardiovascular disease and diabetes, RLP-TG levels were significantly higher than those in normal control subjects. RLP-TG levels increased significantly after an oral fat load and the ratio of RLP-TG/total TG increased > 3-fold compared to the ratio in the fasting state. Approximately 80% of TG increased after an oral fat load was TG derived from remnant lipoproteins. Normal range of plasma RLP-TG in the fasting Japanese population was first determined using a highly sensitive TG assay reagent. RLP-TG was shown to be higher in cases with metabolic syndrome, cardiovascular disease, etc and a better marker than RLP-C for the measurement of postprandial remnant lipoproteins, together with total TG for RLP-TG/total TG ratio.