The dependence of radioimmunoassay detection limits on antibody affinity

Competitive radioimmunoassay standard curves for progesterone were established with tritiated progesterone and six different anti-progesterone monoclonal antibodies ranging in affinity from 1.23 x 10(8) to 2.82 x 10(10) l/mol. The detection limits for these curves ranged from 133 to 6,670 pmol/l final assay concentration (16.7 to 839.1 pg/tube). Separately, a mass-action mathematical model was used to predict lower detection limits for assays run under equivalent conditions with the six antibodies. When compared to the experimental data the predictions were reliable for the higher affinity antibodies but became less accurate as the affinity decreased.