ABSTRACT
According to the new guidelines of the National cholesterol education program [NCEP] for secondary prevention in adults with evidence of coronary heart disease or other atherosclerotic diseases, lipoprotein analysis is required and classification is based on low density lipoprotein cholesterol [LDL-C]. Friedewald equation is the most commonly used approach in clinical laboratories for estimating LDL-C. We studied the reliability of calculated LDL-C by Friedewald formula compared with direct LDL-C measurement. Five fasting samples were collected at 5 days= interval from 50 hyper cholesterolaemic subjects and total cholesterol, triglyceride [Tg] and high density lipoprotein cholesterol [HDL-C] were determined in these samples. LDL-C was calculated by both Friedewald equation and also measured directly with a commercially available direct LDL-C assay. The intra individual CV for the direct and calculated LDL-C assays were similar [CV of direct LDL-C assay [mean "S.E]: 6.9" 0.5% vs calculated LDL-C :7.2" 0.5%, difference: 0.39%, 95% confidence interval: 0.7-1.5%]. Total variability was reduced to < 5% by taking the average of 2 blood tests from each subject. We concluded that conventional calculated LDL-C gave reliable results compared with direct LDL-C assay. However direct LDL-C assay appears more suitable for accurate quantitation of LDL-C in routine laboratories for lipid disorder evaluation and monitoring the treatment because the calculated LDL-C is subject to error with increasing levels of Tg