Comparison between direct estimation of LDL and Friedewald's formula

Background: The reference method for determining LDL-C is b-quantification. It requires ultracentrifugation, uses large volumes of samples and is a time consuming and expensive technique. Therefore, this method is not suitable for routine laboratory testing. The Friedewald’s formula use in routine practice for LDL has many limitation as it is not suitable for TG values >400 mg/dl. Also it tends to underestimate the LDL values. Aim: The aim of this study was to compare the results obtained by direct homogenous assay for LDL-C to those obtained by Friedewald’s formulas with the assumption that the results obtained by direct assay are the most accurate. Materials and methods: Outpatient fasting complete lipid profile (including directly measured LDL) for patients >18 years of age performed between October 2014 and January 2015 was included in the study. A total of 1768 separate fasting lipid profiles were analyzed. Calculated LDL was derived using FF, and directly measured using homogenous assay using liquid selective detergent. Fasting heparin samples were collected Results: It was found that the level of LDL estimated by Friedewald’s formula was significantly lesser than that by direct estimation of LDL. There was a direct positive correlation between LDL by direct method and Friedewald’s formula. Conclusion: Novel and innovative direct homogeneous assays are accurate, precise, fully automated and cost effective. Therefore, for correct cardiac risk classification, direct homogeneous assay should be the method of choice to estimate LDL-C in routine clinical laboratories.