comparison of calculated and direct low density lipoprotein cholesterol determinations in a routine laboratory

Abstract

Background: Low density lipoprotein cholesterol (LDL-C) concentrations form the basis for treatment guidelines established for hyperlipidaemic patients. LDL-C concentrations are commonly calculated using the Friedwald formula (FF) which has several limitations. Recently, direct methods for LDL-C estimation have been developed which are suitable for routine laboratories. Objective: To compare serum LDL-C concentrations determined by a direct assay and the Friedwald formula. Design: Cross-sectional study. Setting: Mater Hospital Laboratory, Nairobi, Kenya. Methods: The clinical performance of the two methods was evaluated by analysing 211 fresh plasma samples from fasting adult patients. The samples were divided into four groups-normolipidaemic; and Types IIa, IIb and IV hyperlipidaemias. Results: The Friedwald formula (FF) correlated best with the direct assay in the normolipidaemic samples (r = 0.879; y= 0.468 + 0.852x). Direct LDL-C values were significantly lower than the FF in the Type IIa hyperlipidaemia samples (paired differences 0.38 ± 0.62). There was only 65% agreement between the two methods in the borderline high LDL-C group of the National Cholesterol Education Program (NCEP) classification (LDL-C 3.36 - 4.14mmol/L). Conclusion: There is lack of agreement between the FF and the Abbott direct LDLC assay. If the two methods are used interchangeably, there may be confusion in the classification and control of lipid lowering medication for patients with hyperlipidaemia