[New clinical application of direct and chemical measurement of low density lipoprotein cholesterol-estimation of compositional changes in triglyceride-rich lipoprotein fraction].

Recently several new direct assay systems for chemical measurement of LDL-cholesterol (Ch) have been developed. These systems allow us to estimate LDL-Ch value even in samples under non-fasting condition as well as samples from prominent hypertriglyceridemics without ultracentrifugation. Since it is possible that the difference between LDL-Ch value measured using new direct method and that calculated using Friedewald's formula can indicate compositional abnormalities of triglyceride-rich lipoprotein (TGRL) fraction (if VLDL-Ch equal to 1/5 of plasma triglyceride, this difference must always be zero), this difference (estimated remnant-Ch) may represent the presence of remnant or intermediate density lipoprotein (IDL) fraction. LDL-Ch is not detected by means of this direct method (LDL-EX, Denka Seiken Co.) in the eluate of the affinity column, which contains anti-apoA1 and anti-B100 antibody, indicating that RLP fraction can be excluded from the assay system. Estimated remnant-Ch correlated well with RLP-Ch, IDL-Ch and apoE. Furthermore, there is no significant correlation between LDL-Ch measured by LDL-EX and Lp(a), indicating that this direct assay system does not include Lp(a) in plasma. Thus, this new direct assay method for LDL-Ch enables us to measure LDL-Ch value with ease and also to estimate compositional abnormalities of TGRL fraction and/or appearance of remnant or IDL fraction without ultracentrifugation.