Some Studies of the Protein-Binding of Steroids and Their Application to the Routine Micro and Ultramicro Measurement of Various Steroids in Body Fluids by Competitive Protein-Binding Radioassay1

A method utilizing the steroid-binding properties of corticosteroid-binding globulin (CBG, transcortin) was described in 1963 for the routine determination of corticoids in 1 ml of plasma (J Clin Endocr23: 293, 1963) and later modified to reduce the time required (J Clin Endocr24: 919, 1964). A 100-fold increase in sensitivity has now been achieved by using tritiated steroids in place of 14C-labeled steroids, by utilizing the CBG's of species other than man, and by using adsorption in place of dialysis or gel filtration. The use of several insoluble adsorbing agents (Fuller's earth, Florisil, coated charcoal) to separate protein-bound and unbound steroids was investigated and their effects on specificity were studied. The use of these techniques in plasma, urine and cerebrospinal fluid was vindicated. With these methods, cortisol can be measured routinely in 0.01 ml of plasma or 0.1 ml of cerebrospinal fluid, and progesterone in 0.3 ml of plasma. Compound S (11-desoxycortisol), corticosterone, cortisone and 11-hydroxyprogesterone can also be measured by this means.