Effect of serum triglycerides on LDL estimation by Friedewald formula and direct assay: a laboratory based study

Abstract

Introduction : A long standing association exists between elevated serum LDL and cardiovascular disease. Studies have suggested that, increased LDL in serum is the major contributor to vascular complications of other diseases like diabetes mellitus, its measurement is recommended in routine clinical practice. Currently, estimation of LDL cholesterol is done in the clinical laboratories using Friedewald equation to make the lipid profile cost effective. However, it has been highlighted that calculated LDL is not reliable when serum triglyceride (TG) levels exceed 400mg/dl. Objective of the study : To compare estimated LDL by homogenous method with calculated LDL by Friedewald equation in lipid profile requests and to compare the same in different groups of triglyceride levels. Materials and Methods : About 260 lipid profile requests of both the genders aged between 25-75 years were considered for the study. Total cholesterol, triglycerides, HDL-cholesterol, LDL -cholesterol was estimated in the serum spectrophotometrically. LDL-C was also calculated using Freidewald formula. The Data thus collected was segregated based on triglycerides into three groups, Group I (TG ?150mg/dl) Group II (TG 151-399 mg/dl) and Group III (TG ?400 mg/dl). Results :LDL determined by direct assay correlated highly with calculated LDL in all subjects irrespective of the TG levels. Correlation coefficients being 0.96, 0.95 and 0.81 in group I, II and III respectively. Estimated LDL was significantlyhigher than the calculated LDL in group II and group III, suggestive of the fact that calculated LDL underestimates the true LDL levels in cases with TG levels above the normal range. Further, the differences in the means were significantly higher in hypertriglyceridemic groups (p 0.001). Conclusion: it can be concluded that estimation of LDL needs a better accurate measurement technique than following calculations, considering the importance of patient care in management of life style disorders, aimed at lowering serum LDL levels.