Enzyme-linked immunosorbent assay for chromogranin A.

This is an enzyme-linked immunosorbent assay (ELISA) for determining chromogranin A (CGA) with use of a monoclonal antibody. CGA was isolated from bovine chromaffin granules. The analytical ELISA procedure for bovine CGA was developed and optimized. Typical standard curves ranged from 500 pg to 500 ng of CGA. We then studied human plasma CGA-immunoreactivity as measured by this assay. The curve for dilutions of human plasma paralleled the standard curve for bovine CGA. The intra-assay coefficient of variation for determination of human plasma CGA was 4.56%, indicating that reliable determinations can be performed for human plasma. However, further study revealed the presence of two CGA-immunoreactive substances in human plasma, one of which corresponds to the native CGA. The nature of the second immunoreactive substance still remains unknown. Nevertheless the measured CGA concentrations (ranging from 0.19 to 0.35 mg/L) in plasma are comparable with previously reported values.