A comparison of urine free cortisol (RIA) with cortisol metabolites (GLC) for detecting increased cortisol secretion

A comparison of the estimation of urine free cortisol by radioimmunoassay with the measurement of cortisol metabolites by gas-liquid chromatography (GLC) for detecting increased adrenal cortical activity has been made. Urine samples were examined from adults with normal or increased adrenal cortical function. Urine free cortisol showed a proportionately greater increase than cortisol metabolites when levels of cortisol were above twice normal, but both procedures led to the same qualitative conclusion about adrenal cortical activity. Their precision, ease of performance, assay time, and cost were similar. It is concluded that the greater sensitivity of the free cortisol does not warrant foregoing the additional information provided by the GLC method.