Measurement of Plasma Cortisol in Children and Adults: A Comparison of the Double Isotope Derivative Assay, Competitive Protein-Binding Analysis and the Modified Competitive Protein-Binding Analysis

Abstract

In normal adults and children, newborn infants and patients with adrenogenital syndrome, plasma cortisol concentrations were measured by double isotope derivative assay (DIDA), competitive protein binding analysis (CPBA), and modified competitive proteinbinding analyis (Modified CPBA). A good correlation was observed between the values obtained in normal adults and children using the DIDA and CPBA; however, a large discrepancy was observed in the values obtained in newborns and patients with the adrenogenital syndrome, the CPBA giving much higher levels. This difference was attributed to the presence in these plasmas of other structurally related steroids which could compete with the binding of cortisol on transcortin. The specificity of the CPBA was improved by a modification involving paper chromatographic purification of cortisol prior to quantification by CPBA. The values thus obtained correspond to the cortisol concentration measured by DIDA and therefore provide a more accurate index of adrenocortical function.