Quantitative determination of human apolipoprotein C-III by electroimmunoassay.

An electroimmunoassay procedure is described for the quantitative determination of human plasma apolipoprotein C-III. Purified apolipoprotein C-III was used for the preparation of monospecific antisera and as the primary standard. This sensitive, specific, rapid (time required for the completion of the assay is 5 h), precise (the within and between-assay coefficients of variation are 6 and 8%, respectively) and accurate electroimmunoassay is applicable to measurement of C-III polypeptide in whole serum and density classes. However, plasma samples containing lipoproteins with Sf less than 400 and/or triacylglycerol levels greater than 700 mg/100 ml must be delipidized. Plasma apolipoprotein C-III levels of normolipidemic subjects and hypercholesterolemic (type IIa) patients were similar (10.4 +/- 3 and 12.0 +/- 6 mg/100 ml, respectively). In contrast, patients with hyperlipoproteinemic phenotypes IIb, III, IV and V had significantly increased levels of apolipoprotein C-III (22 +/- 7; 23 +/- 6, and 54 +/- 12, respectively). The levels of apo C-III in patients with type V were significantly higher (P less than 0.001) than in normal or other hyperlipoproteinemic phenotypes.