Comparison of the Friedewald equation with Martin and Sampson equations for estimating LDL cholesterol in hypertriglyceridemic adults

Abstract

Low density lipoprotein cholesterol (LDL-C) is traditionally calculated using the Friedewald (LDL-F) equation. New equations by Martin (LDL-M) and Sampson (LDL-S) have improved accuracy relative to LDL-F for samples with high triglycerides (TG) or low LDL-C. However, most labs still rely on LDL-F and few studies have examined the accuracy and impact of contemporary LDL-C equations applied to a retrospective dataset. 934 lipid panels with a concurrent direct enzymatic LDL-C (dLDL-C) result were extracted from the laboratory information system. LDL-F, LDL-M, and LDL-S were calculated and the accuracy of each equation determined in a predominantly hypertriglyceridemic population. The impact of implementing each equation was compared by analyzing the LDL-C treatment group miscategorization rate relative to dLDL-C. The slope for the LDL-F, LDL-M and LDL-S were 0.59, 0.78, and 0.94, relative to dLDL-C. The three equations performed comparably for samples with TG <4.52 mmol/L (<400 mg/dL). The LDL-C treatment group miscategorization rate was 48.6 % for LDL-F, 28.8 % for LDL-M and 37.2 % for LDL-S in specimens with TG ≥4.52 mmol/L (≥400 mg/dL) (n = 817). LDL-S underestimated treatment group category (31.3 %, 95 % CI 17.2-22.4) relative to LDL-M (9.0 %, 4.39-7.41, P < 0.001). 5.9 % of samples were overestimated for treatment group category by LDL-S vs 19.8 % for LDL-M (P = 0.1883). LDL-M and LDL-S demonstrate reduced bias with a dLDL-C method compared to LDL-F in samples with TG ≥4.52 mmol/L (≥400 mg/dL). LDL-M reduces LDL-C treatment group miscategorization rate leading to fewer underestimations of risk overall compared to LDL-S; however, neither may be sufficiently accurate to report LDL-C in patients with TG ≥4.52 mmol/L (≥400 mg/dL).

Keywords: Cholesterol; Friedewald; LDL; Lipids.