Comparison of two assays for measuring LDL cholesterol

The purpose of this study was to evaluate the LipiDirect assay (L-LDL) against the Direct LDL(TM) immunoseparation method (D-LDL) and beta quantification (BQ-LDL) for measurement of LDL cholesterol (LDL-C) in patients with normo- and hypertriglyceridemia. Samples from 156 patients [triglyceride (Tg) range 0.61-9.95 g/L] were assayed for LDL-C concentrations with the three methods. An additional seven patients with type III hyperlipidemia and 25 paired sera from fasting and nonfasting individuals also were analyzed by the three methods. Both assays displayed excellent precision. The mean LDL-C value from L-LDL was significantly higher than BQ- LDL and D-LDL in normo- and hypertriglyceridemic samples (P <0.001). The mean absolute bias of L-LDL vs BQ-LDL was 12.7% for Tg <4 g/L and 30.6% for Tg ≤4 g/L, compared with 6.2% and 12.5%, respectively, for D-LDL. L-LDL correctly classified only 68% of patients with LDL-C <1.30 g/L and 57% of patients with LDL-C between 1.30-1.59 g/L as compared with 98% and 93%, respectively, for D-LDL (P <0.001). In patients with type III hyperlipidemia, L-LDL had a 130% positive bias with BQ-LDL as compared with a 14% negative bias for D-LDL. With all three methods there were no significant differences between samples from fasting and nonfasting individuals. On the basis of these findings, the D-LDL assay appears to be superior to the L-LDL assay.