Competitive solid-phase immunoassay of gastrin in serum using time-resolved fluorometry

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BACKGROUND: A competitive solid-phase assay for the measurement of gastrin in serum using time-resolved fluorescence was developed as an alternative to conventional radioimmunoassay (RIA) technology. METHODS: The assay depends on the competitive binding of unlabelled versus Eu-labelled gastrin to specific gastrin antibodies--bound to anti-rabbit IgG immobilized on polystyrene microtitration strips. The bound Eu(3+)-label was dissociated from the bound gastrin and converted to a fluorescent β-diketone chelate which was measured by fluorometry with time-resolution. RESULTS: Using a sample volume of 50 μl the lower limit of detection was below 10 pmol/L. Dilution of samples showed an excellent linearity. Spiking with gastrin-17 in known concentrations showed a recovery of 103% indicating that there is no bias inherent in the assay. The method correlated fully with the routine in-house radioimmunoassay in the concentration range 10-400 pmol/L (slope = 0.98 with r(2) = 0.98). Thus the reference interval for clinical samples does not require modification when changing from one method to the other. CONCLUSION: We have described a convenient and accurate competitive assay for measurement of gastrin in serum based on solid-phase technology using time-resolved fluorometric detection as a realistic alternative to the established state-of-the-art RIA-technology.