Validation of Friedewald, Martin/Hopkins and Sampson Equations in the Low-Density Lipoprotein Cholesterol Estimation with Different Assays

Background Low-density lipoprotein cholesterol (LDL-C) is an important biomarker for determining cardiovascular risk and regulating lipid lowering therapy. Therefore, the accurate estimation of LDL-C concentration is essential in cardiovascular disease diagnosis and prognosis. Sampson recently proposed a new formula for the estimation of LDL-C. However, little is known regarding the validation of this formula. Objectives This study aimed to validate this new formula with other well-known formulas in Turkish population, composed of adults. Methods A total of 88,943 participants above 18 years old at Sivas Cumhuriyet University Hospital (Sivas, Turkey) were included to this study. LDL-C was directly measured by homogeneous assays, i.e., Roche, Beckman and Siemens and estimated by Friedewalds, Martin/Hopkins, extended Martin/Hopkins and Sampsons formulas. The accuracies between the estimations obtained by the formulas and the direct measurements were evaluated both in general and separately for the LDL-C, TG and non-HDL-C sublevels. Linear regression analysis was applied and residual error plots were generated between each estimation and direct measurement method. Coefficient of determination (R2) and mean absolute deviations were also calculated. Results The results showed that the extended Martin/Hopkins approach was the overall most accurate approach for LDL-C estimation. The results also showed that the highest concordances were obtained between the direct assays with the extended Martin/Hopkins formula calculated with the median statistics obtained from our own population. On the other hand, it was observed that the results of the methods may differ in different assays. Although the best performance was obtained by the Sampson formula in patients with "low LDL-C level and hypertriglyceridemia", the extended Martin/Hopkins approach, calculated from the median statistics of our population, gave the most accurate results in patients with "low LDL-C level or hypertriglyceridemia". Conclusions In conclusion, in patients with a low LDL-C level or hypertriglyceridemia, the extended Martin/Hopkins method; in patients with a low LDL-C level and hypertriglyceridemia, the Sampson method may be preferred. The validity of the Martin Hopkins and Sampsons formulas has to be further investigated in different populations.