COMPARISON OF 2 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 q uantification (BQ-LDL) for measurement of LDL, cholesterol (LDL-C) in patients with normo- and hypertriglyceridemia., Samples from 156 patie nts [triglyceride (Tg) range 0.61-9.95 g/L] were assayed for LDL-C con centrations 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 disp layed excellent precision. The mean LDL-C value from L-LDL, was signif icantly higher than BQ-LDL and D-LDL in normo- and hypertriglyceridemi c 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 greater than or equal to 4 g/L, com pared with 6.2% and 12.5%, respectively, for D-LDL. L-LDL correctly cl assified 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%, repect ively, 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% ne gative bias for D-LDL. With all three methods there were no significan t differences between samples from fasting and nonfasting individuals. On the basis of these findings, the D-LDL assay appears to be superio r to the L-LDL assay.