Pitfalls in homogeneous assays for HDL-c and LDL-c in serum]

Between 1994 and 2004, homogenous assays for HDL-C and LDL-C based on different determination principles were developed to replace complicated conventional precipitation methods. Nowadays, most laboratories employ homogenous assays. However, due to differences in principles and reactivity, measurements made by different assays do not necessarily match in some cases. HDL-C determinations may vary depending on duration and conditions of serum storage for the CDC-DCM and the homogenous assay methods, due to their different principles of determination. In patients with cholestasis, apoE-rich HDL, Lp-X and Lp-Y are occasionally observed. In these cases, the reactivity of homogenous assays for HDL-C varies markedly among the manufacturers. Furthermore, because the specific gravities of Lp-X and Lp-Y are comparable to that of LDL, these lipoproteins are grouped as LDL by ultracentrifugation, and this is a source of confusion in clinical settings. The American CDC assesses the accuracy of cholesterol assays by the BQ method, which measures the total of IDL, the narrowly-defined LDL, and Lp(a). However, of the various homogenous assays for LDL-C, reactivities to IDL and Lp (a) differ, and as a result, it is possible that type III hyperlipidemia characterized by increased IDL may be misdiagnosed.