Automated immunoturbidimetric analysis of six plasma apolipoproteins: correlation with radial immunodiffusion assays

We measured six apolipoproteins (apo AI, AII, B, CII, CIII, and E) by turbidimetric method using an automatic discrete biochemical analyzer and commercially available antisera. The turbidimetric method was compared with the single radial immunodiffusion method. Linearity for serum apolipoprotein assay by the automated turbidimetric method was better than by the single immuno-diffusion method. The linearity by the turbidimetric method was 2.5 G/L for AI, 1.0 G/L for AII, 4.5 G/L for B, 0.12 G/L for CII, 0.3 G/L for CIII, and 0.12 G/L for E. The presence of high concentrations of bilirubin (up to 0.15 G/L) and hemoglobin (up to 50 G/L) interfered with apolipoprotein measurement. Comparison of the immunoturbidimetric and the single radial immunodiffusion (SRID) methods showed excellent coefficients of correlation, r = 0.963, 0.896, 0.846, 0.936, 0.972, and 0.937 for apo AI, AII, B, CII, CIII, and E, respectively. Reference ranges for the six apolipoproteins were determined by using sera from 450 healthy subjects and were 1.4 +/- 0.3 G/L for AI and 0.3 +/- 0.01 for E. The observed levels of AII (P less than 0.001), B (P less than 0.01), and CIII (P less than 0.01) were significantly higher in males. The serum levels of apo B, CII, and E showed a gradual increase with age which was more prominent in females than in males. The levels of apo AI, AII decreased significantly over an 11 day period in 22 patients with myocardial infarction.