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Type: Journal article
Title: Plasma free cortisol fraction reflects levels of functioning corticosteroid-binding globulin
Author: Lewis, J.
Bagley, C.
Elder, P.
Bachmann, A.
Torpy, D.
Citation: Clinica Chimica Acta, 2005; 359(1-2):189-194
Publisher: Elsevier Science BV
Issue Date: 2005
ISSN: 0009-8981
Abstract: <h4>Background</h4>In normal plasma free cortisol accounts for less than 6% of the total with 80-90% bound to corticosteroid-binding globulin (CBG) and the remainder associated albumin. However little is known about the distribution of free cortisol in plasma where CBG is inactivated or in congenital CBG deficiency.<h4>Methods and results</h4>Here we describe ligand binding experiments revealing that while free cortisol in unstressed individuals is less than 6% of total cortisol this rises markedly to 25% when CBG is totally inactivated by heat. Similar elevations of the free cortisol fraction were noted in a patient with a rare genetically determined complete lack of CBG (mean 32% on frequent circadian sampling). Following heat inactivation of CBG or in the congenital absence of CBG, there is a shift in cortisol binding from CBG to albumin. That this shift occurs is further supported by experiments adding [3H]-cortisol to physiological human serum albumin solutions, where 25% of cortisol remained in the free fraction.<h4>Conclusion</h4>Taken together the data provide strong evidence that when CBG is inactivated or congenitally absent then more than 25% of the total cortisol appears in the free fraction with the remainder associated with albumin. The proportion of free cortisol measured in plasma thus reflects a simple measure of functional corticosteroid-binding globulin.
Keywords: Humans; Hydrocortisone; Serum Albumin; Transcortin; Ligands; Enzyme-Linked Immunosorbent Assay
RMID: 0020050930
DOI: 10.1016/j.cccn.2005.03.044
Appears in Collections:Medicine publications

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