Evaluation of alternative calculation methods for determining LDL cholesterol.

BACKGROUND Due to limitations of the Friedewald formula, alternative methods for calculating low-density lipoprotein cholesterol (LDL-C) were suggested. We evaluated utility of these methods. METHODS Ninety three subjects free of coronary heart disease were considered. LDL-C was measured by the homogeneous method, and calculated by the Friedewald formula LDL-C = TC-HDL-(TG/2.2) (LDL1) and alternative formulas LDL-C = 0.41 TC - 0.32 TG + 1.70 apoB - 0.27 (LDL2) and LDL-C = 0.94 TC - 0.94 HDL - 0.435 TG (LDL3). RESULTS All three formulas underestimated the measured LDL-C, both in the whole group and in subgroups according to TG levels (TG < 1.7 and in a range of 1.7-4.5 mmol/l, p < 0.001 for all). We found significantly higher bias for all three formulas in subjects with 1.7 < or = TG < 4.5 mmol/l levels. The Friedewald formula showed the lowest assay bias in all the groups investigated. The mean absolute bias for LDL1 was 7.6%, 18.3% for LDL2 and 13.6% for LDL3, respectively. Linear regression analysis showed correlation of calculated LDL-C values with the direct method in the range of r = 0.82 - 0.90 (p < 0.0001 for all, except of LDL2 in 1.7 < or = TG < 4.5 mmol/l group where p = 0.0011). CONCLUSIONS The Friedewald formula seems to be a better estimator of LDL-C in our study than the other two alternative formulas; however, it underestimated the LDL-C levels.