Laboratory validation of a low density lipoprotein apolipoprotein-B assay

Objectives: Numerous publications have shown strong association between CHD risk and either apolipoprotein B (Apo-B) or low density lipoprotein (LDL) particle number (LDL-P). It is however unknown if Apo-B or LDL-P has a stronger predictive ability for future CHD. This uncertainty may be due to the inability of current Apo-B assays to separate the contribution of very low-density lipoprotein particles from the total Apo-B concentration. As such we have performed a laboratory validation of the Maine Standards (R) LDL Apo-B assay on the Roche Cobas 6000 analyzer. Design and methods: Imprecision, linear range, and limit of quantitation studies were performed using quality control materials. Plasma samples collected for lipid profile analysis were analyzed via the LDL Apo-B assay and compared to the LDL cholesterol (LDL-C) concentration determined via direct LDL assay and Friedewald equation. Results: The LDL Apo-B within-run imprecision was 23% at 62 mg/dL and 2.2% at 109 mg/dL. The within-laboratory imprecision was 9.7% at 57 mg/dl and 6.1% at 104 mg/dl. Linear regression analysis of LDL Apo-B versus calculated and measured LDL-c resulted in equations of LDL Apo-B = 0.620 (*) (LDL) + 45.4, R = 0.9063 and LDL-Apo-B = 0.607 (*) (LDL) + 38.8, R = 0.9393, respectively. Bias plot analyses revealed that at low LDL-C concentration, there was a tendency for a higher than anticipated LDL Apo-B concentration. Conclusions: The Maine Standards LDL Apo-B assay is a precise automated assay and comparison of LDL ApoB to LDL-c concentration demonstrates that low LDL-C concentrations may still carry residual risk of CHD due to increased concentration of small dense LDL particles. (C) 2014 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.