Comparison between two methods for measuring serum low density lipoprotein cholesterol

ABSTRACT

Two methods for low density lipoprotein cholesterol [LDL-C]. estimation were compared at different triglycerides [TG] levels. These were the quantitative determination by Helena cellulose acetate electrophoresis methods and the indirect calculation using Friedwald formula. Eighty fasting samples were selected and classified into 4 groups according to their TG levels. LDL-C was determined in each sample by both methods. Strongly significant correlation coefficients, between the 2 methods were obtained at normal, slightly, and moderately increased TG levels [r = 0.99, 0.97 and 0.94 respectively]. At TG levels >350 mg/dl the correlation became much weaker [r =0.77]. Thirty samples at different TG levels, were examined in duplicate for accuracy and precision. The electrophoretic quantitation of LDL-C was, much more precise [CV = 2.6%] than the indirectly calculated one. The latter depends on the imprecision of methods used in measuring total cholesterol, TG and HDL-C by precipitation method [CV = 2.7%, 3.8% and 8.5% respectively]. Paired t test showed no significant difference between LDL-C values obtained by both methods [P>0.05] However, in all cases of hypertriglyceridemia, the calculated LDL-C values showed constant insignificant lower values [6 - 12% lower] which might be sufficiently erroneous to cause misinterpretation of hypercholesterolemia at the critical LDL-C levels when medical interventions required. We recommended using the Fridewald formula as a screening test for LDL-C estimation and the electrophoresis method at TG levels> 350 mg/dl, LDL-C levels> 200 mg/dl or when abnormal lipoproteins are present