J.G.TAN1, G.E.D.LAPENA1, M.P.H.ER1, P.Y.HENG1, M.S.WONG1
Khoo Teck Puat Hospital1
In 2019, cardiovascular disease accounted for 29.3% of all deaths in Singapore. The association between lower exposure to LDL-Cholesterol (LDLC) and greater reduction in cardiovascular disease risk is consistently demonstrated by randomized controlled trials, prospective cohort and Mendelian randomization studies. Currently, most laboratories use the Friedewald formula developed in 1972 to estimate LDLC. More recently, Martin et al 2013 and Sampson et al 2020 have published new equations for the calculation of LDLC. We seek to evaluate the performance of these new equations and the original Friedewald formula against measured LDLC.
Triglycerides, Total Cholesterol, measured LDLC (mLDLC) and HDL-Cholesterol were analyzed on the Cobas c702 analyser (Roche Diagnostics). A total of 1594 results was obtained from the Laboratory Information System for June 2021. Passing Bablok regression and Bland Altman analysis were performed using MedCalc Version 20 (Ostend, Belgium).
The following Passing Bablok regressions and Spearman’s coefficients (ρ) were obtained: LDLC-Friedewald = 0.969*mLDLC – 0.167, ρ=0.978; LDLC-Martin = 0.947*mLDLC – 0.100, ρ=0.984; LDLC-Sampson = 0.972*mLDLC – 0.123, ρ=0.985.
The mean differences were -0.274, -0.233, -0.203 mmol/L when compared to mLDLC for Friedewald, Martin and Sampson equations respectively. The 95% upper and lower limits of agreement were [-0.710 to 0.161, -0.622 to 0.156, -0.577 to 0.171] respectively.
LDLC calculated by all three equations are lower than mLDLC, with the values obtained by Sampson equation most similar to mLDLC. The Sampson equation may be superior to the commonly used Friedewald formula and may substitute the more costly measurement of mLDLC in resource-poor settings.