Immunoassays for serum C-reactive protein employing fluorophore-labelled reactants

Two simple rapid and precise fluorescence assays for determining serum levels of C-reactive protein (CRP) are described which employ sheep antibodies to CRP covalently linked to magnetisable cellulose/iron oxide particles. The first (a fluoroimmunoassay) is based on competitive binding of CRP in the sample or standard with fluorescein-labelled CRP, a 30 min incubation time, simple separation with a magnet followed by elution of the bound fraction into alkaline methanol and fluorescence quantitation. In the second (a 'sandwich' immunofluorometric assay) an excess of solid-phase linked antiserum is incubated with sample and fluorescein-labelled purified sheep anti-CRP immunoglobulin followed by separation, elution and quantitation of the bound fraction. The assays cover the ranges 3-400 mg/l and 3-70 mg/l respectively and the results correlate well with those obtained by radial immunodiffusion and radioimmunoassay.