Comparison of Four Formulas for Calculating LDL-Cholesterol with the Direct Homogeneous Method

Background/Objectives: Low-density lipoprotein cholesterol (LDL-C) is a primary therapeutic target in cardiovascular risk assessment. While direct assays are available, LDL-C is frequently estimated using various formulas, whose performance can vary by population and lipid concentration. This study evaluates the analytical agreement and clinical classification performance of four formulas (Spasić–Kotur–Vujović, Friedewald, De Long, and Martin–Hopkins) against directly measured LDL-C. Methods: Lipid profiles from 3935 fasting adult patients were analyzed. LDL-C was directly measured via a homogeneous assay and compared with calculated values using linear regression and Bland–Altman analyses. Analytical bias and classification accuracy were assessed across stratified lipid levels. Results: Among the evaluated equations, the Spasić–Kotur–Vujović formula showed the closest agreement with directly measured LDL-C. It had the lowest mean absolute bias and mean percentage differences across most lipid strata, as well as narrower limits of agreement compared with Friedewald, De Long, and Martin–Hopkins formulas. Although all formulas showed strong correlations with directly measured LDL-C (Pearson’s r correlation coefficient = 0.956–0.958; intraclass correlation coefficient > 0.974), systematic underestimation of LDL-C was observed for all equations and became more pronounced with increasing total cholesterol, LDL-C, triglycerides, and non-high-density lipoprotein cholesterol concentrations. The Spasić–Kotur–Vujović formula achieved the highest overall classification accuracy (70%), followed by De Long (68%), Martin–Hopkins (61%), and Friedewald (58%). Conclusions: Despite strong correlations, clinically relevant differences in bias and classification exist among LDL-C formulas. The Spasić–Kotur–Vujović formula demonstrated superior agreement and accuracy in this population, suggesting it is a more reliable tool for routine laboratory practice. It should be noted that these findings reflect agreement with the specific homogeneous LDL-C assay used on the Alinity c platform (Abbott Laboratories,, Chicago, IL, USA) and may not be directly generalizable to other analytical systems.