Discordance Between Standard Equations for Determination of LDL Cholesterol in Patients With Atherosclerosis

Background: Accurate estimation of low-density lipoprotein cholesterol (LDL-C) is important for guiding cholesterol-lowering therapy. Different methods currently exist to estimate LDL-C. Objectives: This study sought to assess discordance of estimated LDL-C using the Friedewald, Sampson, and Martin/Hopkins equations. Methods: Electronic health record data from patients with atherosclerotic cardiovascular disease and triglyceride (TG) levels of <400 mg/dL between October 1, 2015, and June 30, 2019, were retrospectively analyzed. LDL-C was estimated using the Friedewald, Sampson, and Martin/Hopkins equations. Patients were categorized as concordant if LDL-C was <70 mg/dL with each pairwise comparison of equations and as discordant if LDL-C was <70 mg/dL for the index equation and ≥70 mg/dL for the comparator. Results: The study included 146,106 patients with atherosclerotic cardiovascular disease (mean age: 68 years; 56% male; 91% White). The Martin/Hopkins equation consistently estimated higher LDL-C values than the Friedewald and Sampson equations. Discordance rates were 15% for the Friedewald vs Martin/Hopkins comparison, 9% for the Friedewald vs Sampson comparison, and 7% for the Sampson vs Martin/Hopkins comparison. Discordance increased at lower LDL-C cutpoints and in those with elevated TG levels. Among patients with TG levels of ≥150 mg/dL, a >10 mg/dL difference in LDL-C was present in 67%, 27%, and 23% of patients when comparing the Friedewald vs Martin/Hopkins, Friedewald vs Sampson, and Sampson vs Martin/Hopkins equations, respectively. Conclusions: Clinically meaningful differences in estimated LDL-C exist among equations, particularly at TG levels of ≥150 mg/dL and/or lower LDL-C levels. Reliance on the Friedewald and Sampson equations may result in the underestimation and undertreatment of LDL-C in those at increased risk.