Comparison of a new method for the direct and simultaneous assessment of LDL- and HDL-cholesterol with ultracentrifugation and established methods

Background: Automated electrophoresis combined with enzymatic cholesterol s taining might improve routine assessment of LDL- and HDL-cholesterol (LDLC and HDLC), as an alternative to the Friedewald equation and precipitation. A new method (Hydrasys; SEBIA) that adapts the cholesterol esterase/cholest erol oxidase reaction within urea-free gels was evaluated. Methods: Fresh sera from 725 subjects (512 dyslipidemics) were analyzed by electrophoresis, in parallel with sequential ultracentrifugation, beta-quan tification, calculation, and precipitation. Results: Electrophoresis was linear up to 4 g/L cholesterol, with a detecti on limit of 0.042 g/L cholesterol/band. Within-run, between-run, between-ba tch, and between-operator imprecision (CVs) were 1.6%, 2.0%, 1.5%, and 2.7% for LDLC, and 3.9%, 4.3%, 5.5%, and 4.9% for HDLC, and remained unchanged up to 6.3 g/L plasma triglycerides (TGs). Precision decreased with very low HDLC (<0.25 g/L). Serum storage far 3-7 days at +4 or -80 OC did not inter fere significantly with the assay. Agreement with beta-quantification was s table for LDLC up to 5.07 g/L (r = 0.94), even at TG concentrations >4 g/L (r = 0.91). Bias (2.88% +/- 12%) and total error (7.84%) were unchanged at TG concentrations up to 18.5 g/L. Electrophoresis predicted National Choles terol Education Program cut-points with <0.04 g/L error, exactly and approp riately classified 79% and 96% of the subjects, and divided by 2.4 (all sub jects) and 5.8 (TGs >1.5 g/L) the percentage of subjects underestimated by calculation. One-half of the patients with TGs >4 g/L had LDLC >1.30 g/L. F or HDLC, correlation was better with precipitation (r = 0.87) than ultracen trifugation (r 0.76). Error (-0.10% +/- 26%) increased when HDLC decreased (<0.35 g/L). Direct assessment of the LDLC/HDLC ratio detected 45% more hig h-risk subjects than the calculation/precipitation combination. Conclusions: Electrophoresis provides reliable quantification of LDLC, impr oving precision, accuracy, and concordance over calculation, particularly w ith increasing plasma TGs. Implementation of methods to detect low choleste rol concentrations could extend the applications for HDLC assessment. (C) 2 000 American Association for Clinical Chemistry.