How Much “UFC” Is Really Cortisol?

Abstract

When urinary free cortisol (UFC) determinations became readily available for clinical use in 1968 (1), chromatographic methods were cumbersome. The first competitive protein-binding method (radiotransinassay) (1) used human corticosteroid-binding globulin (transcortin) as the binding protein. The specificity of the assay was enhanced by the use of Fuller’s earth as the agent to adsorb the unbound fraction because it takes up some of the competing steroids differentially (2). The reference interval was ∼10–100 μg/day (30–300 nmol/day). When radioimmunoassays, based on the same competitive binding principle but using antibodies raised to cortisol linked to albumin, became popular during the 1970s, it was assumed that these would be more specific for cortisol, but this assumption was not warranted. As pointed out recently (3), most of the articles published over the past 20 years have quoted even higher values, reflecting a significant lack of specificity. In 1976, Chattoraj et al. (4) found values for UFC after combined thin-layer and column chromatography that were approximately one-half those of the original method (1), as did Schoneshofer et …