Correlation, Agreement, and Treatment Misclassification of Sampson and Friedewald Equations for Estimated LDL-Cholesterol Across Triglyceride Levels

Abstract

   Objectives: Concordance between calculated and directly measured LDL- C levels, as assessed by various measures of test accuracy (correlation coefficient, Bland-Altman plot and percentage of patients misclassified at LDL-C treatment thresholds).

   Methods: The study was conducted on data from 1277 subjects who measured all four lipid tests (triglycerides, total cholesterol, LDL-C, HDL-C). The LDL-C level measured by β-quantification derived method and the calculated LDL-C using formulas (Sampson, Friedewald) were analyzed for Pearson correlation with the correlation coefficient and regression equations. The agreement was assessed using Bland-Altman plots, and the percentage of patients misclassified at LDL-C treatment thresholds was evaluated using Cohen’s Kappa statistic.

   Results: The  Sampson  equation  exhibited  a  stronger  correlation compared to the Friedewald equation (r = 0.892, p < 0.05, vs. r = 0.814, p < 0.05). In the triglyceride (TG) < 200 mg/dL group, the Sampson and the Friedewald equation demonstrated high agreement, with %Mean LDLdiff values of 3.18% and 5.19%, respectively. In the 200 ≤ TG < 400 mg/dL group, only the Sampson formula maintained an acceptable level of agreement (%Mean LDLdiff = 11.98%), whereas the Friedewald formula showed a higher %Mean LDLdiff of 18.78%. In the highest TG group, both formulas exhibited significant discrepancies, with %Mean LDLdiff values of 27.93% and 43.05%, respectively.

   Conclusions: LDL-C calculated using both the Sampson and Friedewald formulas exhibits a strong correlation with direct LDL-C. The Sampson equation maintains an acceptable level of agreement in the TG < 400 mg/dL group, whereas the Friedewald equation is only acceptable in the TG < 200 mg/dL group. The correlation and agreement of both formulas are inversely proportional to TG levels.

DOI: 10.59715/pntjmp.4.3.14