A-241 Effect of remnant cholesterol to low density lipoprotein cholesterol (LDL-C) ratio on the accuracy of direct LDL-C measurement

Abstract Background The reference method of low density lipoprotein cholesterol (LDL-C) measurement is beta-quantification, composing of three step including ultracentrifugation, precipitation and cholesterol measurement by Abell-Kendall method. The method is time-consuming, laborious and demands large volume of samples, which limits its use in clinical laboratories. Consequently, Friedewald equation for LDL-C estimation has been widely used owing to its simplicity and usefulness in routine and epidemiologic use. Direct homogenous methods for LDL-C, performed rapidly without preparation and fully automated, were also developed and are widely implicated in routine uses. Although direct measurement can be a good alternative, the reliability of the method has been challenged since some reagents also detect a part of cholesterol presented in the chylomicron and very-low density lipoprotein, also known as remnant cholesterol. In this study, we aimed to investigate the effect of remnant cholesterols on the results of LDL-C measured by homogenous methods. Methods This study used 41 commutable frozen serum samples which were produced following Clinical and Laboratory Standards Institute C37-A guideline. These 41 samples were used for the Korean quality assurance program of manufacturers for lipid assays during 2023-2024. In this program, the Korea Disease Control and Prevention Agency (KDCA) provide two vials of each sample to participating manufacturers. The manufacturers measure total cholesterol (TC), LDL-C, high density lipoprotein cholesterol (HDL-C), and triglyceride (TG) from each vial in two different days in triplicate and submit the results to KDCA. Roche, Beckman Coulter, Siemens, Abbott, Fujifilm Wako, Minaris, Sekisui, and Diasys participated this program and submitted the result of TC, HDL-C, LDL-C, and TG in the 41 samples. These manufacturers are anonymized as A, B, C, D, E, F, G, and H, respectively. The reference value of TC, HDL-C, LDL-C, and TG were also determined by reference methods. Remnant cholesterol levels were calculated from reference values using the formula: Remnant cholesterol = TC – HDL-C – LDL-C. The LDL-C measurement bias (%) of each manufacturer relative to the reference value was calculated for each sample. The relationship between the remnant cholesterol/LDL-C ratio and LDL-C %bias was assessed using Spearman’s correlation analysis. Results The mean remnant cholesterol/LDL-C ratio of 41 samples was 0.22, with individual ratios ranging from 0.08 to 0.68. Correlation analyses were performed to assess the relationship between the remnant cholesterol/LDL-C ratio and direct LDL-C measurement %bias (Figure 1). Statistically significant positive correlations were observed in six of the eight manufacturers (Figure 1. B–E, G, H). For samples with a remnant cholesterol/LDL-C ratio of < 0.25 (n=31), directly measured LDL-C demonstrated showed minimal bias. In contrast, for samples with a remnant cholesterol/LDL-C ratio of 0.25 or higher (n=10), most reagents exhibited greater %bias. Conclusion This study underscores that remnant cholesterol can serve as a significant source of positive bias in direct LDL-C measurement, which varies by reagents. Clinical laboratories should be aware of this potential interference, especially in samples with elevated remnant cholesterol levels. In addition, the reagents that exhibited notable bias associated with remnant cholesterol should prioritize refining their methodologies to minimize remnant cholesterol interference.