[Determination of hydrocortisone in human blood plasma using competitive binding with endogenous transcortin].

A direct express-method is developed for estimation of hydrocortisone, based on the use of individual human blood plasma endogenous transcortine as a binding system. The method is designed for non-serial estimation of hydrocortisone in human blood plasma and may be used for an express-analysis, since extraction of the hormone from blood plasma by organic solvents is omitted. The dissociation constant of the transcortine-hydrocortisone complex was calculated using Scatchard plot. On the basis of this procedure and considering the rule of acting masses the initial concentration of receptor sites was measured for transcortine at a given blood plasma dilution and theoretical curves were constructed for the reaction of competitive substitution of labelled hydrocortisone by the unlabelled hormone. Estimation of hydrocortisone, carried out by means of these theoretical curves of substitution, closely correlated with the data of experimental standard curves of substitution (CEA-IRE-Sorin). The express-method of hydrocortisone estimation was used in clinical research.