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Published on: October 12, 2017
Laboratory validation of a low density lipoprotein apolipoprotein-B assay
David E Kelsey1, Jessica L Toher1, Michael T Foster2
1Maine Standards Company, Windham, ME, USA.
Insights
This study validated a new assay for apolipoprotein B (Apo-B), finding it precise for predicting coronary heart disease (CHD) risk. Low LDL cholesterol may still indicate residual risk due to small dense LDL particles.
Area of Science:
- Cardiovascular diagnostics
- Clinical chemistry
Background:
- Coronary heart disease (CHD) risk is strongly associated with apolipoprotein B (Apo-B) and low-density lipoprotein (LDL) particle number (LDL-P).
- The comparative predictive ability of Apo-B versus LDL-P for future CHD remains unclear.
- Current Apo-B assays may not accurately distinguish very-low-density lipoprotein contributions, potentially affecting predictive accuracy.
Purpose of the Study:
- To perform a laboratory validation of the Maine Standards LDL Apo-B assay on the Roche Cobas 6000 analyzer.
- To assess the precision and analytical performance of the LDL Apo-B assay.
- To compare LDL Apo-B concentrations with LDL cholesterol (LDL-C) levels.
Main Methods:
- Validation studies included imprecision, linear range, and limit of quantitation using quality control materials.
- Plasma samples were analyzed using the LDL Apo-B assay.
- Results were compared to direct LDL-C measurements and LDL-C calculated via the Friedewald equation.
Main Results:
- The LDL Apo-B assay demonstrated good within-run imprecision (2.2-2.3%) and acceptable within-laboratory imprecision (6.1-9.7%).
- Linear regression showed strong correlations between LDL Apo-B and both measured (R=0.9393) and calculated (R=0.9063) LDL-C.
- Bias plots indicated higher-than-expected LDL Apo-B concentrations at low LDL-C levels.
Conclusions:
- The Maine Standards LDL Apo-B assay is a precise and automated method for quantifying LDL Apo-B.
- The assay's comparison with LDL-C highlights that low LDL-C may not fully capture CHD risk.
- Elevated small dense LDL particles, indicated by higher LDL Apo-B at low LDL-C, may represent residual CHD risk.
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 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 2.3% 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 Apo-B 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.
