Simple enzyme immunoassay for the measurement of immunoreactive chromogranin A in human plasma, urine and saliva

Abstract

A simple and sensitive enzyme immunoassay (EIA) was developed for determining human chromogranin A (CgA)-like immunoreactivity (IR) with use of synthetic human CgA (344-374) as antigen. In the development of the present EIA system, purposely designed Na-biotinylated glycylglycyl-human CgA (344-374), which was synthesized, was proved to be a useful biotinylated derivative. Typical standard curves ranged from 13.7 fmol/mL to 10 pmol/mL of CgA-like IR. In the present EIA, the curves for dilution of human plasma, urine, and saliva paralleled the standard curve for synthetic human CgA (344-374). The intra-assay coefficient of variation for measurement of human plasma CgA was from 2.6% to 8.5%, indicating that reliable determinations can be performed for human plasma. The levels of CgA-like IR were 0.34 ± 0.08 pmol/mL (mean ± SD, n = 10) in fasting normal plasma, 0.18 ± 0.05 pmol/mL (n = 8) in urine, and 0.11 ± 0.05 pmol/mL (n = 8) in saliva in the morning are comparable with the respective values in RIA reported in the previous papers.