The measurement of free cortisol, free testosterone and free oestradiol-17beta: a comparison of five different methods
Kley, H.K.; Bartmann, E.; Krüskemper, H.L.
Journal of Clinical Chemistry and Clinical Biochemistry 15(9): 465-472
1977
ISSN/ISBN: 0340-076X PMID: 925632 Document Number: 123521
Five methods for the determination of free cortisol, testosterone and estradiol-17.beta. in plasma at 37.degree. C are compared: equilibrium dialysis with undiluted plasma, equilibrium dialysis with 1:5 diluted plasma using a conversion factor to establish the free fraction in undiluted plasma (correlation r:0.95), equilibrium dialysis using graphical analysis for the establishment of the free steroid fraction inundiluted plasma (r:0.90), zonal chromatography (r:0.92) and centrifugal filtration (r:0.80). The concentrations of the free hormones were measured by the above 5 methods in plasma from each of the following groups: healthy young males, healthy females, females taking hormonal contraceptives and pregnant women. Zonal chromatography was best suited when judged by the precision of the method. This was especially true when high binding and low plasma concentration of a steroid were present. Equilibrium dialysis with undiluted plasma was well suited for clinical purposes in both its precision and practicability. Centrifugal filtration and graphic analysis of the equilibrium dialysis method were less recommendable, because of variation of the results at high binding. Normal values of total and free hormone concentrations of cortisol, testosterone and estradiol are given for the collectives studied. It is possible to compare the values obtained by different laboratories when different methods are used to determine the free steroid fractions of cortisol, testosterone and estradiol.