Evaluation of an automated radioimmunoassay for serum cortisol

The performance characteristics are reported for a serum cortisol assay using the GAMMAFLO Automated Assay System, an automated continuous-flow system for radioimmunoassay (RIA). This automated system utilizes a combination of continuous-flow methodology and column chromatography techniques. The cortisol assay studied had a standard curve range of 10.0 to 500 microgram per L. The intra-assay and inter-assay precision were 5.1 percent and 7.2 percent (RSD), respectively, for a cortisol concentration of 160 microgram per L. The automated serum cortisol results correlated (r = 0.958 and 0.933) with two established manual radioimmunoassay procedures. No drift or carryover was detectable in 200 within-assay consecutive determinations performed at a rate of 42 determinations per hour (five hours continuous operation). The automated system studied appears to offer a viable alternative to cortisol manual RIA techniques in terms of overall precision simplicity of operation, and sample throughput.