The measurement of serum cortisol by a solid-phase chemiluminescence immunoassay

A solid-phase chemiluminescent immunoassay (LIA) for the determination of cortisol in serum specimens has been developed. The separation of the cortisol onto the solid-phase distinguishes this particular assay from other chemiluminescence immunoassays. The method can be used without prior extraction. Cortisol molecules were made chemiluminescent by conjugation to aminobutylethyl-isoluminol. The detection limit of the label in the chemiluminescent reaction was 0.1 pmol. The LIA was compared with a RIA for cortisol in 36 serum specimens and the correlation between the assays was good (r = 0.97). The time course of the chemiluminescent reaction is fast and a 20's integration time gave reproducible results. The peak light intensities were not reliable.