A Comparative Study of Methods of Estimation of LDL-Cholesterol: Direct vs Friedewald's Formula and Their Impact on the Risk Assessment for Coronary Artery Diseases

Abstract

Coronary artery disease is one of the leading causes of mortality and morbidity worldwide. Correct estimation of low density lipoprotein (LDL) cholesterol is not only fundamental but also imperative towards the right diagnosis, risk assessment and management of the patients of cardiac diseases. Many laboratories rely on the calculated method of LDL-C estimation. Direct assays are now replacing the calculated methods owing to some of the limitations of the latter. We carried out a comparative study to evaluate the reliability of both the methods and their impact on assessing cardiac risk. Fasting lipid profile (including TG, Total Cholesterol, LDL-C and HDL-C) was measured by direct enzymatic assays in serum samples of 200 patients who visited the Biochemistry Laboratory for this test. LDL-C was also estimated by Friedewald's formula. Results of LDL-C obtained by two methods were compared and statistically analysed. We found a significant positive correlation between the values of LDL-C obtained by two methods i.e. Friedewald's formula and Direct Assay. Friedewald's formula underestimated the actual LDL-C levels especially when the serum TG levels were high and this difference was significant when the TG levels were >400 mg/dL. Thus, some of our patients who were having high cardiac risk (LDL-C >130 mg/dL) were misdiagnosed to be normal. Friedewald's formula can be used for LDL-C estimation when TG levels are in the normal range but results become doubtful especially when the serum TG levels are high. Direct assay has an advantage that it is not influenced by the concordant serum TG concentrations and can be relied upon confidently in determining cardiac risks in the individuals.