Measurement of serum free cortisol shows discordant responsivity to stress and dynamic evaluation.
BACKGROUND
Routinely available assays of adrenal function measure serum total cortisol (TC) and not the biologically active free cortisol (FC). However, there are few data on FC levels during surgical stress and in response to standard pharmacological tests.


OBJECTIVE
Our objective was to evaluate TC and FC levels in different states of physical stress.


METHODS
We conducted a prospective observational study in a university hospital.


METHODS
We measured TC and FC levels in 64 patients: group A, 17 healthy controls without stress; group B, 23 medical patients with moderate stress; and group C, 24 surgical patients undergoing coronary bypass grafting. Cortisol levels in group C were measured basally and at several time points thereafter and were compared with responsivity to a pharmacological dose of ACTH. FC was measured using equilibrium dialysis.


RESULTS
In group C patients after extubation, the relative increase above basal FC was higher than the increase in TC levels (399 +/- 266 vs. 247 +/- 132% of initial values, respectively; mean +/- sd; P = 0.02) and then fell more markedly, FC levels falling to 67 +/- 49% and TC levels to 79 +/- 36% (P = 0.04). After ACTH stimulation, TC levels increased to 680 +/- 168 nmol/liter, which was similar to the increase with major stress (811 +/- 268 nmol/liter). In contrast, FC levels increased to 55 +/- 16 nmol/liter after ACTH stimulation but significantly greater with surgical stress to 108 +/- 56 nmol/liter (P < 0.001).


CONCLUSIONS
The more pronounced increase in FC seen during stress as compared with the ACTH test suggests that this test does not adequately anticipate the FC levels needed during severe stress.
Christ-Crain
Mirjam
M
Department of Endocrinology, Barts and The London, Queen Mary's School of Medicine, University of London, London, United Kingdom. christmj@bluewin.ch
Jutla
Sukhdeep
S
Widmer
Isabelle
I
Couppis
Orestes
O
König
Caroline
C
Pargger
Hans
H
Puder
Jardena
J
Edwards
Ray
R
Müller
Beat
B
Grossman
Ashley B
AB
D000304:Adrenal Cortex Function Tests; D000324:Adrenocorticotropic Hormone; D000328:Adult; D000368:Aged; D001026:Coronary Artery Bypass / Q000009:adverse effects*; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000097:blood*; D007124:Immunoenzyme Techniques; D007239:Infections / Q000097:blood; D007249:Inflammation / Q000097:blood; D049449:Luminescence; D008297:Male; D008875:Middle Aged; D011184:Postoperative Period; D011446:Prospective Studies; D044967:Serum / Q000737:chemistry / Q000378:metabolism; D013312:Stress, Physiological / Q000097:blood* / Q000209:etiology; D014156:Transcortin / Q000378:metabolism
D000324:Adrenocorticotropic Hormone; D014156:Transcortin; D006854:Hydrocortisone