Sequential fluoroimmunoassay for measurement of pregnancy specific β 1 glycoprotein using antibody coupled to magnetisable particles

Abstract

A direct, sequential fluoroimmunoassay has been developed for the determination of serum levels of pregnancy specific β 1 glycoprotein (SP 1). The method employs rabbit anti-SP 1 serum coupled to magnetisable cellulose-iron oxide particles and fluorescein-labelled Sp 1. Serum samples or standards are incubated with magnetisable solid phase anti-SP 1 for 30 min. After magnetic sedimentation of the particles, the supernate, which includes endogenous fluorophores and other interfering factors, is discarded. Fluorescein-labelled SP 1 is then added and incubated for a further 45 min; the particles are again sedimented and the fluorescence of the labelled SP 1 remaining in the supemate is estimated. This reading relates directly to the SP 1 content of the original sample. The entire procedure, including fluorometry, is performed within a single disposable polystyrene test tube and is sufficiently simple and reliable for routine application. The sensitivity, specificity and precision is very similar to that of radioimmunoassay, and the results correlate closely with those of the radioimmunoassay ( r = 0.9887).