Comparison between Values of Low Density Lipoprotein Cholesterol as Estimated by Direct Enzymatic Method with Calculated Methods Applying Friedewald’s Equation and Novel’s Equation: A Cross-sectional Study

Introduction: Lipid profile is routinely used as a screening test to identify the risk of Cardiovascular Diseases (CVD). Elevated Low Density Lipoprotein cholesterol (LDL-c) is an important modifiable risk factor of atherosclerotic CVD. The LDL-c lowering strategy is a known recommendation for the prevention and treatment of CVD. The gold standard method of LDL-c estimation is β-quantification by ultra centrifugation. Other methods include Direct LDL-c measurement (D-LDL-c) using enzymatic assay which is tedious, time consuming and expensive. Hence, calculated method using Friedewald’s equation (F-LDL-c) is routinely used in clinical laboratories in India. Aim: To compare LDL-c values as estimated by direct enzymatic method with LDL-c values obtained by Friedewald’s equation and Novel’s equation, and, also to assess the effects of LDL-c values obtained by both the methods towards the risk stratification of CVD. Materials and Methods: A cross-sectional study, was conducted in the Central Diagnostic Laboratory of Mandya Institute of Medical Sciences, Mandya, Karnataka, India, for a duration of three months from July to September 2020, where, 600 subjects, aged 20-75 years, visiting for routine lipid profile estimation were included. LDL-c was estimated by direct enzymatic method (D-LDL-c) and calculated methods using Friedewald’s {F-LDL-c=TC-HDL-c- (TG/5)} and Novel’s equation {N-LDL-c=TC-HDL-c-(TG/Adjustable factor)}. Values obtained by calculated methods were compared with D-LDL-c values. The LDL-c values obtained were compared at different ranges of Total Cholesterol (TC), Triglycerides (TG) and High-Density Lipoprotein cholesterol (HDL-c). The association between direct and calculated LDL-c values were analysed by Pearson’s correlation. Receiver Operator Characteristic Curve (ROC) analysis was done to predict the better diagnostic method among the calculated methods of LDL-c. Results: The mean±SD of D-LDL-c (115.68±36.94 mg/dL) was high compared to F-LDL-c (106.95±33.48 mg/dL) and N-LDL-c (110.78±32.58 mg/dL). The mean difference between D-LDL-c and N-LDL-c (4.9±4.36 mg/dL) was low compared to F-LDL-c (8.75±3.46 mg/dL). Significant positive correlation was observed between D-LDL-c vs F-LDL-c (r=0.96; p=