COMPARISON OF AN IMMUNOPRECIPITATION METHOD FOR DIRECT MEASUREMENT OFLDL-CHOLESTEROL WITH BETA-QUANTIFICATION (ULTRACENTRIFUGATION)

A direct LDL cholesterol assay was evaluated using immonoprecipitation (Sigma Diagnostics, St. Louis, MO) with beta-quantification obtained by ultracentrifugation. Excellent intra- and interassay coefficients o f variation were obtained (< 4.5%). There was a good correlation (r = 0.88, P < .0001) between the two methods for low-density lipoprotein c holesterol (LDL-C) in 249 samples with triglyceride levels ranging fro m 13 mg/dL to 2,236 mg/dL and LDL cholesterol levels ranging from 28 m g/dL to 290 mg/dL. Similar correlations were seen for patients with tr iglyceride bevels < 400 mg/dL (r = 0.89, n = 174) and greater than or equal to 400 mg/dL (r = 0.89, n = 75). However, using the Friedewald e quation, there was a good correlation only in samples with triglycerid e levels < 400 mg/dL. No significant differences were found between LD L-C quantitated by the direct LDL assay and beta quantification for pa tients with dysbetalipoproteinemia (Type III disorder). However, calcu lated LDL values using the Friedewald equation were found to be signif icantly higher when compared to beta-quantification in patients with t he Type III disorder. There was a slight but significant decrease in L DL-C determined by direct LDI, cholesterol assay for non-fasting versu s fasting serum (4.7%) despite a strong correlation between these samp les (r = 0.98, P < .0001). In addition, freezing samples for 30 days r esulted in a significant decrease in levels (15.1%). Thus, this direct LDL cholesterol assay is recommended in plate of beta-quantification in hypertriglyceridemic samples (TG greater than or equal to 400 mg/dL ) and to monitor LDL cholesterol levels in patients with Type III dysl ipidemia, because it is less time consuming, more cost-effective and c an be adapted to the clinical laboratory.