Estimation of Serum Apolipoprotein B by a Modified Homogeneous Assay for HDL-Cholesterol

Serum lipoprotein analysis frequently is used in assessing the risk for coronary artery disease and for monitoring cholesterol-lowering therapy (1)(2). A recent improvement in the analysis of lipoproteins is the development of homogeneous assays for HDL-cholesterol (HDL-C) (3)(4) that are easier to perform because they do not require the physical separation of the apolipoprotein B (apoB)-containing lipoproteins by precipitation and centrifugation. The measurement of LDL-cholesterol (LDL-C) and apoB, the principal protein on LDL, is also useful for estimating the risk for cardiovascular risk (1)(2). An isolated increase in apoB in the absence of increased total cholesterol and LDL-C is diagnostic for a risk condition called hyperapoB-lipoproteinemia (5). We describe a simple modification of an antibody-based commercial homogeneous assay for HDL-C (EZ-HDL; Sigma Diagnostics) that in addition to measuring HDL-C, also provides an estimate of the apoB concentration. In step 1 of the EZ-HDL assay, an anti-apoB antibody is added, which binds to the surface of the apoB-containing …