Comparison of various low density lipoprotein cholesterol calculators. Is it time for the Friedewald equation to go?
Authors: Dorairaj P , Chandran H 
Published: October 2022

Abstract

Aim
Plasma low density lipoprotein cholesterol (LDL-C) is a unit measure of cholesterol mass & an estimate of circulating LDL-C. LDL-C is commonly calculated indirectly by Friedewald equation and not directly with enzymatic method. The Friedewald equation underestimates the LDLC compared to direct LDLC particularly in patients with low LDLC and high Triglycerides (TGL). Recently developed Sampson equation (2020) also estimates LDL-C indirectly but is less dependent on the TGL values. The present study compares directly measured LDL-C with above friedewald and sampsons equations.

Methodology
A Multicentric study (three health centers) measured LDL-C with direct enzymatic method in 8332 samples. The data was collected using electronic database and computed in Microsoft excel. Retrospective analysis was performed after ethical committee approval and waiver of consent. LDL-C values derived from Friedewald equation & Sampson equation was compared with LDL-C from direct enzymatic method. Subgroup analysis for accuracy was done among various direct LDL-C subgroups such as values less than 50 mg/dl, 50–70 mg/dl, 70–150 mg/dl and more than 150 mg/dl. The entire cohort was also subdivided into triglyceride subgroups &lt;150 mg/dl, 150–450 mg/dl, &gt;450 mg/dl and compared with direct LDL-C values.

Results
Our study results shows that mean direct LDL-C was 85.7mg/dl, mean calculated LDL-C by Sampson and Friedewald equation were 80mg/dl and 76mg/dl respectively. There was statistical significance in mean difference when direct LDL-C is compared with combined Sampson and Friedewald equation as per Games - Howell multiple comparison study in which mean difference was more with Friedewal's equation than with Sampson equation. The overall concordance upwards between Friedewald's equation versus direct LDL-C and Sampson LDL-C equation versus direct LDL-C was similar (81% and 83% respectively). The overall discordance upwards was more with Sampson LDL-C when compared with direct LDL-C (4%), unlike 1.5% when Friedewald's LDL-C compared with direct LDL-C. The overall discordance downwards was less with Sampson's LDL-C when compared with direct LDL-C (12%) unlike, 16% when Friedewald's LDL-C compared with direct LDL-C. Our study showed that mean LDL-C by Friedewald's equation is less accurate in comparison to the mean direct LDL-C values. But mean LDL-C by Sampson equation had close proximity to mean direct LDL-C values and less magnitude of discordance was noted in patients with low LDL-C & high TGL

Conclusions
Sampson's equation is better than friedewald's equation in estimation of LDL-C. Sampson's equation is ideal, better, easily calculated and incorporated. We have also developed a simple android application to estimate the LDL-C using both the Sampson and the Friedewald equation. We recommend that sampson's equation can be utilized in third world developing countries in planning low LDL-C targets during secondary prevention.

Funding Acknowledgement
Type of funding sources: None.