Comparison of competitive protein binding radioassay of cortisol to double isotope dilution and porter silber methods

The competitive protein binding radioassay of corticoids was performed on 4 pools of plasma, and the results compared to those obtained on the same pools by paper chromatography and protein binding, double isotope dilution, and colorimetric (Porter-Silber reaction) techniques. In the low and normal ranges, the colorimetric method was the only one significantly different, i.e., higher. In the high ranges the colorimetric method was significantly higher; while the paper chromatography and protein binding techniques were significantly lower than the protein binding radioassay for corticoids.