The role of immunochemistry in the direct measurement of low density lipoprotein cholesterol

The concentration of low density lipoprotein cholesterol (LDL-C) is the primary parameter for diagnosis of coronary heart disease and for the determination of appropriate therapy. The development of an assay that would directly measure LDL-C would be an improvement over the current method of estimating LDL-C by the Friedewald equation, which requires the measurement of total cholesterol, total triglycerides, and high-density lipoprotein cholesterol and which has some serious clinical limitations. The Direct LDL-C(TM) assay uses latex bead-bound antibodies against human apolipoproteins A-I and E to separate LDL from other lipoproteins, The assay requires only a single measurement of cholesterol which can be made on essentially any clinical analyzer. In seven clinical evaluations, the performance parameters of the Direct LDL-C assay were generally equivalent to the Friedewald equation for specimens for which the Friedewald equation was appropriate and/or to the beta-quantification method. Precision, accuracy, and the ability to classify specimens into risk categories were similar. The Direct LDL-C assay surpasses the clinical usefulness of the Friedewald equation in that it is appropriate for use,vith specimens from nonfasted or type III dyslipoproteinemic patients and requires only 30 mu L of specimen. Hypertriglyceridemia has variable effects on the Direct LDL-C assay and may cause overestimation of LDL-C in some specimens with triglycerides between about 400 and 800 mg/dL. The improvement of the Direct LDL-C assay over the Friedewald equation is basically one of convenience rather than analytical superiority for most specimens.