Evaluation of different formulas for LDL-C calculation

Abstract

Background: Friedewald's formula for the estimation of LDL-C concentration is the most often used formula in clinical practice. A recent formula by Anandaraja and colleagues for LDL-C estimation still needs to be evaluated before it is extensively applied in diagnosis. In the present study we validated existing formulas and derived a more accurate formula to determine LDL-C in a Serbian population.

Methods: Our study included 2053 patients with TG < or = 4.52 mmol/L. In an initial group of 1010 patients, Friedewald's and Anandaraja's formulas were compared to a direct homogenous method for LDL-C determination. The obtained results allowed us to modify Friedewald's formula and apply it in a second group of patients.

Results: The mean LDL-C concentrations were 3.9 +/- 1.09 mmol/L, 3.63 +/- 1.06 mmol/L and 3.72 +/- 1.04 mmol/L measured by a direct homogenous assay (D-LDL-C), calculated by Friedewald's formula (F-LDL-C) and calculated by Anandaraja's formula (A-LDL-C), respectively in the 1010 patients. The Student's paired t-test showed that D-LDL-C values were significantly higher than F-LDL-C and A-LDL-C values (p < 0.001). The Passing-Bablok regression analysis indicated good correlation between calculated and measured LDL-Cs (r > 0.89). Using lipoprotein values from the initial group we modified Friedewald's formula by replacing the term 2.2 with 3. The new modified formula for LDL-C estimation (S-LDL-C) showed no statistically significant difference compared to D-LDL-C. The absolute bias between these two methods was -0.06 +/- 0.37 mmol/L with a high correlation coefficient (r = 0.96).

Conclusions: Our modified formula for LDL-C estimation appears to be more accurate than both Friedewald's and Anandaraja's formulas when applied to a Serbian population.

Figure 1

Distribution of percentage differences for the Friedewald's, Anandaraja's and Serbian formula (Ff, Af and Sf, respectively) in the validation group.

Figure 2

Mean percentage differences for Friedewald's (Ff), Anandaraja's (Af) and our modified (Sf) formula according to TC (A), TG (B) and LDL-C (C) cut-off values proposed by NCEP ATP III in the validation group.