The development of a direct homologous radioimmunoassay for serum cortisol.

This article describes the synthesis of a pure cortisol-3-(O-carboxymethyl) oxime with its subsequent use in producing highly specific antibodies and a 125I-tracer with a shelf life in excess of several weeks. An assay was developed using a pH of 4, thus allowing a direct measurement of cortisol in serum without extraction or heat denaturation. The quality-control parameters were checked - the intra-assay C.V. in the working range (area of clinical interest) was under 5%, and the interassay C.V. under 11%. Correlation studies with results using other antisera and with 3H-tracer are highly significant with the slope of the regression curve deviating less than 2% from the ideal volume. Finally the assay is fully automatable and is suitable for most automatic pipetting and analysis systems.