Does LDL-C Estimation Using Anandaraja's Formula Give a Better Agreement with Direct LDL-C Estimation than the Friedewald's Formula?

Estimation of low density lipoprotein cholesterol (LDL-C) is crucial in management of coronary artery disease patients. Though a number of homogenous assays are available for estimation of LDL-C, use of calculated LDL-C by Friedewald's formula (FF) is common in Indian laboratories for logistic reasons. Recently Anandaraja and colleagues have derived a new formula for calculating LDL-C. This formula needs to be evaluated before it is extensively applied in diagnosis. We measured LDL-C by homogenous method (D-LDL-C) in 515 fasting samples. Friedewald's and Anandaraja's formulas were used for calculation of LDL-C (F-LDL-C and A-LDL-C, respectively). The mean LDL-C levels were 123.3 +/- 53.2, 112.4 +/- 50.2 and 109.2 +/- 49.8 mg/dl for D-LDL-C, F-LDL-C and A-LDL-C, respectively. There was a statistically significant difference between the results (P < 0.001) obtained by calculation formulas compared to the measured LDL-C. There was underestimation of LDL-C by 10.8 and 14 mg/dl by Friedewald's and Anandaraja's formulas respectively. The Pearson's correlation between F-LDL-C and D-LDL-C was 0.931 and that between A-LDL-C and D-LDL-C was 0.930. Bland-Altman graphs showed a definite agreement between mean and differences of the calculation formulas and direct LDL-C with 95% of values lying with in +/- 2 SD limits. The mean percentage difference (calculated as {(Calculated LDL-C)-(D-LDL-C)}/ D-LDL-C 9 100) for F-LDL-C was maximum (-11.6%) at HDL-C >= 60 mg/dl and TG levels of 200-300 mg/dl (-10.4%) compared to D-LDL-C. A-LDL-Cresults gave highest mean percentage difference at total cholesterol concentrations >100 mg/dl (-37.3%) and HDL-C >40 mg/dl (-17.1%), respectively. The results of our study showed that FF is better in agreement with D-LDLC than Anandaraja's formula for estimation of LDL-C by calculation though both lead to its underestimation.