A comparison of direct measurement of low density lipoprotein cholesterol level in serum with standard Friedewald, De-Long and modified Friedewald equation

Reduction of low density lipoprotein cholesterol (LDL-C) in persons with coronary heart disease (CHD) is targeted. First step in treatment of lowering the LDL-C level is lifestyle modification including diet, weight reduction and exercise. At second step, the lipid lowering drug should be added. Although direct measurement of LDL-C from serum is most accurate, but it is not cost-effective, so laboratories usually use the Friedewald equation that suffers from several limitations such as hypertriglyceridemia and variability of lipoprotein composition. The authors compared and determined the correlation of LDL-C from enzymatic measurement with LDL-C from calculating. A total of 475 fasting serum samples (199 males and 276 females with mean age of 56.3 years) with TG less than 400 mg/ dl in Imam Hossein hospital (Shahroud) were analyzed. According to serum TG levels, samples divided in four groups (<100, 100-199, 200-299, 300-400). Authors calculated the LDL-C and then compared with direct measurement. Data analyzed with SPSS and table curve packages. The comparison between direct and calculated methods showed that: 1) Concordance with the difference of 0±20 mg/dl is low. 2) Friedewald showed more accuracy compared with other calculated methods (51.2% versus 38.7% and 42.7%). 3) with the raising of TG, the accuracy declines and the overestimation increases. Correlation coefficient was 0.66. An overestimation of approximately 0±20 mg/dl was found in over 50% of samples comparison with direct LDL-C. Therefore; direct measurement of LDL-C in patients with CHD is recommented.