Multicentric evaluation of the homogeneous LDL-cholesterol Plus assay: Comparison with beta-quantification and Friedewald formula

Objectives To evaluate the analytical and clinical performance of a new version of the LDL-C Plus assay and compare it with the beta-quantification (BQ) method in a multicenter study. Design and methods Direct LDL-C was measured in 169 fresh pooled samples and in 830 clinical samples with known LDL-C by BQ. The reactivity of lipoproteins and the effect of hemoglobin, bilirubin and chylomicrons (CM) were studied. Results Direct LDL-C total imprecision was < 2.2%; inaccuracy < ± 2.5% (unaffected by triglycerides up to 9.5 mmol/L); and total error 9.8%. Direct assay reacted with 95%, 50% and 25% of the cholesterol in the LDL, intermediate (IDL) and VLDL fractions, respectively. A significant association was observed with BQ. Icteric samples showed a negative bias and the effect of CM was variable. A positive bias was observed when VLDL-cholesterol/triglyceride ratio was > 0.57. Conclusions LDL-C Plus assay represents a valid alternative to BQ for clinical laboratories.