Quantification of apolipoprotein A-IV in human plasma by immunonephelometry

We developed a nephelometric procedure for determining concentrations of human plasma apolipoprotein (apo) A-IV. Results obtained correlate well with those measured by an established electroimmunodiffusion assay (r = 0.98; n = 56). Intra- and interassay CVs were 2.4% and 2.0%, respectively, indicating excellent precision and reproducibility. Various conditions of sample treatment, such as adequate storage, freezing, and thawing, did not affect results significantly. However, keeping samples at room temperature for 4 days led to a slight increase in measured values. Preincubation with a cholesterinesterase-detergent mixture abolished interference from triglyceride-rich lipoproteins, allowing assay of samples containing triglycerides as great as 10 g/L. The assay is easily applicable to clinical laboratories for routine diagnostic use, as shown with hypertriglyceridemic plasmas and samples with a broad range of apo A-IV concentrations.