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Journal of Clinical Endocrinology & Metabolism , doi:10.1210/jc.2006-2361
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Right arrow Adrenal and Hypertension
The Journal of Clinical Endocrinology & Metabolism Vol. 92, No. 5 1729-1735
Copyright © 2007 by The Endocrine Society

Measurement of Serum Free Cortisol Shows Discordant Responsivity to Stress and Dynamic Evaluation

Mirjam Christ-Crain1, Sukhdeep Jutla1, Isabelle Widmer, Orestes Couppis, Caroline König, Hans Pargger, Jardena Puder, Ray Edwards, Beat Müller and Ashley B. Grossman

Department of Endocrinology (M.C.-C., S.J., O.C., A.B.G.), Barts and The London, Queen Mary’s School of Medicine, University of London, London E1 2AD, United Kingdom; NETRIA (R.E.), St. Bartholomew’s Hospital, London EC1A 7BE, United Kingdom; and Department of Endocrinology (I.W., C.K., B.M.) and Surgical Intensive Care (H.P.), University Hospitals, CH-4031 Basel, Switzerland; and Department of Endocrinology (J.P.), University Hospital, CH-1011 Lausanne, Switzerland

Address all correspondence and requests for reprints to: Dr. M. Christ-Crain, Department of Endocrinology, Barts and The London, Queen Mary’s School of Medicine, University of London, London E1 2AD, United Kingdom. E-mail: christmj{at}bluewin.ch.


   Abstract
Top
 Abstract
Introduction
 Patients and Methods
 Results
 Discussion
 References
 
Context: 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.

Design and Setting: We conducted a prospective observational study in a university hospital.

Participants and Main Outcome Measures: 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).

Conclusion: 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.


   Introduction
Top
 Abstract
 Introduction
Patients and Methods
 Results
 Discussion
 References
 
CORTISOL CIRCULATES IN blood largely bound to corticosteroid-binding protein (CBG) and albumin (1), with the much smaller amount of unbound hormone responsible for its metabolic effects (1, 2, 3, 4). In general, it is assumed that the biologically active level of cortisol to which tissues are exposed is free cortisol (FC). Routinely available assays of adrenal function measure serum total cortisol (TC) and not the biologically active FC, but it is usually considered that TC broadly correlates with the biologically free fraction. However, it has been shown that in critically ill patients there is a fall in binding proteins such that TC levels no longer accurately reflect the free fraction, and this could potentially cause misdiagnosis of adrenal function (5, 6).

Peri- and postoperative basal cortisol levels reflect the degree of surgical stress (7, 8), with peak cortisol levels being achieved in the immediate postoperative period, around the time of extubation (9, 10). Serum TC levels after major surgery approach the levels during the acute phase of septic shock (11, 12, 13). In this context, major surgery can serve as a standardized model for studying acute and major stress. In patients undergoing major surgery, the importance of the fall in CBG on measured serum TC concentrations has recently been recognized (14), and the authors of this study recommended the use of a calculated correction factor, the FC index, defined as the serum cortisol concentration divided by the CBG concentration, as a surrogate marker to better define glucocorticoid secretion (14). However, the FC index does not take into account the effect of hypoalbuminemia, which often accompanies low serum concentrations of CBG, and thus does not measure the actual serum FC concentration (6). Previous studies have also demonstrated that under the most stressful conditions, TC levels in response to major stress are mirrored by similar changes in the response to a pharmacological dose of ACTH (15). It has therefore been assumed that responsivity to the ACTH stimulation test will reflect the pituitary-adrenal response to surgery, trauma, or other types of stress and can be used as a surrogate to decide on the appropriateness of corticosteroid replacement therapy in surgery or acute illness (16) in the absence of recent pituitary surgery (17).

We have developed a new direct, simple, and robust serum FC assay and have used it to assess whether the responsivity to a standard dynamic test of adrenal function does indeed reflect the adrenal response to surgical stress. Our results suggest that there are serious defects in predicting FC reserve from the response to ACTH.


   Patients and Methods
Top
 Abstract
 Introduction
 Patients and Methods
Results
 Discussion
 References
 
Setting and study population

Sixty-four participants with different levels of physical stress were included (Table 1Go) (15). Ethical approval was obtained and the patients or their legal representatives gave written informed consent to participate in the study. Group A (no stress) contained 17 healthy control subjects, mainly staff members. Group B (moderate stress) consisted of 23 patients consecutively recruited from a wide and representative variety of nonhypertensive patients having been hospitalized on the medical ward for various reasons, i.e. acute diabetic complications (hyperglycemic crisis or hypoglycemia), infections (urosepsis, exacerbation of chronic obstructive lung disease, or pneumonia), inflammation (acute pancreatitis or myocarditis), hypoventilation syndrome, myocardial infarction, congestive heart failure, unstable angina pectoris, cerebrovascular insult, decompensated liver cirrhosis, and ocular neuropathy. None of the patients showed clinical or laboratory features of acute or chronic adrenal insufficiency. Group C consisted of 24 stable surgical patients consecutively recruited from the Division of Cardiothoracic Surgery undergoing elective coronary artery bypass grafting under general anesthesia. These patients served as a standardized model for changing stress levels. We speculated that on the morning before operation there would be no or only minimal apparent stress, and during the operation the stress would increase, whereas maximal stress to activate the pituitary-adrenal axis would be present after extubation, with partial resolution on the following morning. This was based on previous detailed studies of the changes in serum cortisol during and after surgery (7, 8, 9, 10). For premedication, midazolam 7.5 mg was used in all surgical patients. Anesthesia was induced with thiopentone (2–4 mg/kg) and fentanyl (2–4 µg/kg); etomidate, which is known to cause changes in adrenal steroidogenesis, was not used (18). Intubation was facilitated with pancuronium (0.15 mg/kg). Before and during cardiopulmonary bypass, anesthesia was maintained with isoflurane (0.5–1.5 minimal alveolar concentration) and fentanyl. During weaning and after bypass, a continuous dormicum-fentanyl infusion was used for maintenance of anesthesia. Routine monitoring included a continuous two-lead electrocardiogram, pulse oximetry, end-tidal CO2 concentration, invasive arterial pressure, and central venous pressure. Antibiotic prophylaxis consisted of cefuroxime (1.5 g, three times per day) for 48 h. Surgery was performed under normothermic conditions (i.e. resulting in cooling not lower than 35 C). Cardiopulmonary bypass was started after heparin (350 IU/kg) and cyclocapron 30 mg/kg using a hollow-fiber oxygenator in all patients. Myocardial preservation during bypass was achieved with intermittent infusion of Bretschneider’s cardioplegic solution. No blood transfusion was required in any patient. The duration of the operation (incision-suture time) was on average 4 h. The number of vessels grafted was 3.6 ± 0.8. At the time of extubation (6–10 h after surgery), 57% of patients needed various amounts of catecholamines, usually epinephrine (1–10 µg/min) and/or norepinephrine (1–10 µg/min). Treatment with catecholamines was necessary in a decreasing manner for a total of 25 ± 4 h (mean ± SD). The median intensive care unit stay was 2 d, and no patient stayed longer than 4 d. None of the patients received corticosteroid treatment. The study design and patients’ characteristics have been described previously (15). Exclusion criteria were as follows: contraindication to receiving synthetic ACTH (i.e. allergies), patients who received drugs that influence the hypothalamo-pituitary-adrenal (HPA) axis during the last 3 months, patients with diseases affecting the adrenal or the pituitary gland, patients with known or suspected primary or secondary adrenal insufficiency, and patients receiving etomidate (19, 20).


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  		TABLE 1. Characteristics of the study group (groups A–C)

 
Study design

In groups A and B, patients were tested on a single occasion between 0600 h and 0900 h. Surgical patients in group C were evaluated at four different time points reflecting different levels of stress: C1, the morning (0600–0900 h) before operation; C2, during operation, 30 min after intubation; C3, 30 min after extubation; and C4, the morning after extubation (0600–0900 h). From previous studies (7, 8) (9, 10), it was anticipated that C3 would show maximal activation of cortisol levels.

According to the original protocol (15), each participant of groups A–C was randomly assigned to be stimulated with either 1 or 250 µg ACTH by block randomization in groups of four and was blinded regarding his/her assignment. Standard ACTH stimulating tests were performed using 250 µg tetracosactidum (Synacthen; Novartis Pharma, Basel, Switzerland; known as Cosyntropin in North America) and 1 µg tetracosactidum [0.25 mg tetracosactidum (Synacthen; Novartis Pharma)] divided into 0.001-mg tetracosactidum doses by the pharmacy of the Kantonsspital (Luzern, Switzerland), as previously described (21, 22). In all subjects, blood samples were taken at time zero for the basal measurement of TC and FC and ACTH and again at time 30 min for measurement of serum TC and FC concentration after iv administration of 1 or 250 µg Synacthen [synthetic ACTH(1–24)], respectively.

Assays

Serum TC was measured using a chemiluminescence immunoassay (Nichols Advantage; Nichols Institute Diagnostics, San Juan Capistrano, CA) with a calculated sensitivity of 13.8 nmol/liter. The intraassay coefficient of variance was 4.4%, and the interassay coefficient of variance was 11.0%.

Serum FC was measured in-house by a specially developed assay. The fractions of free and bound cortisol in serum samples were first separated by equilibrium dialysis, followed by measurement of the concentration of the free fraction in the dialysate using an enzyme immunoassay (NETRIA, London, UK). Dialysis was carried out using a membrane with a molecular weight cutoff of 12,000–14,000 Da, and 200 µl undiluted sample was pipetted directly into dialysis tubing (diameter ~6 mm), sealed at one end, and placed into an outer chamber (diameter 12 mm) containing 800 µl buffer solution (pH 7.4) of 1% hydrolyzed gelatin in PBS (0.05 M phosphate, 0.15 M sodium chloride). Dialysis chambers were gently rotated at 37 C overnight. Dialysate containing the free fraction was assayed by enzyme immunoassay.

The calculated sensitivity of the enzyme immunoassay (96-well microtiter plates coated with anticortisol antiserum) was 0.4 nmol/liter (at 2.5 SD from zero cortisol concentration). The interassay coefficients of variance were 3.5% at 2.1 nmol/liter, 6.8% at 24 nmol/liter, and 10.0% at 52 nmol/liter. Intraassay coefficient of variance was assessed by precision profile with the following coefficients of variance: 10% at 1 nmol/liter, 6% at 10 nmol/liter, 5% at 20 nmol/liter, and 7% at 100 nmol/liter.

Relative potencies of cross-reacting steroids were measured as follows: corticosterone, 9%; 11-deoxycortisol, 2%; 17-{alpha} hydroxyprogesterone, 1.4%; prednisolone, 53%; cortisone, 1.4%; 11-deoxycorticosterone, 0.2%; progesterone, 0.1%; and dexamethasone, testosterone, 17ß-estradiol, tetrahydrocortisol, and cholesterol, less than 0.1%. The assay was validated in 12 patients with confirmed adrenocortical insufficiency (TC, 134.1 ± 134 nmol/liter). Free cortisol levels in these patients were 2.7 ± 2.5 nmol/liter, significantly lower compared with FC levels in healthy controls (36.9 ± 17.2 nmol/liter) (all P values < 0.001).

Albumin was measured by Hitachi 917 (Roche, Rotkreuz, Switzerland). CBG was measured by a RIA (BioSource Europe, S.A., Nivelles, Belgium). The FC index was calculated by dividing serum TC by the CBG (nanomoles per milligram). Procalcitonin was measured by a time-resolved amplified cryptate emission technology assay (Kryptor PCT; Brahms AG, Hennigsdorf, Germany). C-reactive protein was measured by an enzyme immunoassay (EMIT; Merck Diagnostica, Zurich, Switzerland).

Statistical analysis

Discrete variables are expressed as counts (percentage) and continuous variables as means ± SD or median (interquartile range), unless stated otherwise. Two-group comparison of normally distributed data was performed by Student’s t test. For multigroup comparisons, one-way ANOVA with least square difference for post hoc comparison was applied. For data not normally distributed, the Mann-Whitney U test was used if only two groups were compared and the Kruskal-Wallis one-way ANOVA if more than two groups were being compared. Correlation analyses were performed by using Spearman rank correlation. All testing was two-tailed, and P values < 0.05 were considered to indicate statistical significance. "NS" indicates not significant.


   Results
Top
 Abstract
 Introduction
 Patients and Methods
 Results
Discussion
 References
 
Table 1Go shows demographic and other characteristics of the subjects in groups A–C (15). There were no differences in age or sex between the groups randomized to the 1 µg or the 250-µg ACTH stimulation test within groups A–C (P = NS in all groups). Therefore, the results of both genders were pooled for additional analysis.

Basal and stimulated TC and FC concentrations in different stress levels

Basal TC levels in controls were 496.1 ± 132 nmol/liter and in the medical patients 468.5 ± 143 nmol/liter; in the surgical patients on the morning before operation, they were 382.0 ± 159 nmol/liter, during the operation 532.7 ± 400 nmol/liter, after extubation 811.4 ± 268 nmol/liter, and the day after operation 604.4 ± 288 nmol/liter (P < 0.001). The respective FC levels were 36.9 ± 17.2, 43.5 ± 18.9, 34.8 ± 16.9, 31.3 ± 26.4, 107.8 ± 55.8 and 63.6 ± 39.3 nmol/liter (P < 0.001 for ANOVA) (Fig. 1Go, A and B). The respective post-ACTH TC and FC levels are shown in Fig. 2Go, A and B.


Figure 1
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  		FIG. 1. TC (A) and FC (B) levels in controls, medical patients, and surgical patients at the four different time points (C1, before the operation; C2, during the operation; C3, after extubation; C4, 1 d after the operation). Small rectangles/squares denote means, larger rectangles/squares SEM, and whiskers 1.96 SEM of the combined data.

 

Figure 2
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  		FIG. 2. TC (A) and FC (B) levels after ACTH stimulation in controls, medical patients, and surgical patients at the four different time points (C1, before the operation; C2, during the operation; C3, after extubation; C4, 1 d after the operation). Small rectangles/squares denote means, larger rectangles/squares SEM, and whiskers 1.96 SEM of the combined data.

 
Post hoc analyses revealed significantly higher TC and FC levels after extubation compared with all other groups. There was no significant difference for TC levels between the control group, medical patients, and surgical patients at baseline, before operation, or the day after operation.

Basal TC and FC concentrations upon major stress

FC levels increased after extubation (i.e. major stress) to 399.1 ± 266% of initial values (P < 0.001 compared with baseline), whereas TC levels increased to 247.1 ± 132% of initial values (P < 0.001 compared with baseline). The percentage increase in FC levels was significantly more pronounced compared with the increase in TC levels (P = 0.02). The FC index (TC/CBG) increased to 335.5 ± 181.2%. FC levels decreased the day after extubation to 66.7 ± 49% of levels after extubation (P = 0.003). TC levels decreased to 79.4 ± 36% of levels after extubation (P = 0.01). The decrease in FC levels was significantly more pronounced compared with TC levels (P = 0.04). The FC index decreased to 78.7 ± 34%. In surgical patients with major stress, FC levels correlated significantly with the calculated FC index (r2 = 0.59; P < 0.001).

Comparison between the increase in basal cortisol levels in major stress and the increase upon stimulation with ACTH in a nonstressed situation

In surgical patients at baseline, the increase in basal FC and TC levels with either 1 or 250 µg ACTH was not significantly different, and we therefore pooled the data. After ACTH stimulation, TC levels increased to 679.9 ± 168 nmol/liter, which was not significantly different from that seen after major stress (811.4 ± 268; P = NS). FC levels increased to 107.8 ± 56 nmol/liter with major stress after extubation, markedly and significantly higher than after ACTH stimulation (55.1 ± 16 nmol/liter, P < 0.001) (Fig. 3Go, A and B).


Figure 3
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  		FIG. 3. TC (A) and FC (B) levels in surgical patients without stress (before operation) after ACTH testing (left) compared with levels upon major stress (after extubation, right). The median level is shown with dot plots representing the absolute values.

 
Percentage of FC to TC in different stress conditions

Under basal conditions in surgical (group C) patients, the percentage of basal FC to basal TC was 9.1 ± 3.0%. With major surgical stress after extubation, this percentage of FC to TC increased to 13.1 ± 3.9% (P < 0.001).

Albumin and CBG with major stress in surgical patients

Albumin levels in surgical patients before operation were 41.0 ± 3.6 mg/liter, during operation 21.7 ± 3.4 mg/liter, after extubation 23.8 ± 2.6 mg/liter, and the day after extubation 23.4 ± 2.3 mg/liter (P < 0.001). Serum CBG levels at the respective time points were 27.7 ± 7.5, 26.1 ± 7.9, 19.3 ± 3.9, and 19.8 ± 4.9 mg/liter (P < 0.001). Post hoc analysis revealed a significant decrease in albumin, but not in CBG, during the operation (for comparison between C1 and C, P < 0.001 and 0.34, respectively). For CBG, post hoc analysis revealed a significant decrease after extubation (for comparison between C2 and C3, P < 0.001), whereas there was no significant decrease in albumin levels (P for comparison between C2 and C3 = NS) (Fig. 4Go, A and B).


Figure 4
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  		FIG. 4. Albumin (A) and CBG (B) levels surgical patients at the four different time points (C1, before the operation; C2, during the operation; C3, after extubation; C4, 1 d after the operation). Small rectangles/squares denote means, larger rectangles/squares SEM, and whiskers 1.96 SEM of the combined data.

 
Difference between 1-µg and 250-µg stimulation test

In the control group, and in medical patients and surgical patients before operation, the percentage increases in FC or TC levels were similar after 1 or 250 µg ACTH, respectively (data not shown). In surgical patients after extubation, TC levels increased to 931.7 ± 231 nmol/liter after 1 µg (P = 0.03) and to 1186.1 ± 327 nmol/liter after 250 µg ACTH (P = 0.01). FC levels increased to 123.3 ± 42 nmol/liter after 1 µg ACTH (P = 0.04) and to 163.8 ± 51 nmol/liter after 250 µg (P = 0.01). The increase with 250 µg ACTH was more pronounced compared with the increase with 1 µg ACTH for FC (P = 0.01) but not for TC.

Correlation of TC and FC levels with parameters of inflammation/infection

C-reactive protein and procalcitonin levels as parameters of inflammation and infection showed a significant increase with surgery [P < 0.01 comparing before surgery (group C1) to after extubation or the day after extubation (groups C3 and C4)]. There was a significant correlation of TC and FC with C-reactive protein and procalcitonin levels (r = 0.45 and 0.39 for TC, and r = 0.55 and 0.60 for FC).


   Discussion
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Discussion
References
 
This standardized model for studying cortisol responsivity to acute major surgical stress shows two main findings. First, serum FC levels show a more pronounced increase with major stress compared with TC levels followed by a more pronounced decrease after resolution of major stress. However, the second critical finding is that whereas TC levels show a similar increase with major stress compared with ACTH stimulation, the increase in FC was more pronounced than with the surgical stress.

The purpose of a stimulation test of the HPA axis is to predict whether, on demand, the adrenals will be able to produce the cortisol levels needed, those actually found in severe stress (16). In normal subjects, the ACTH test correctly seems to predict the TC levels that will be reached under severe stress in most cases (15). Conversely, our results suggest that the serum TC response to ACTH does not accurately reflect maximal HPA axis reserve, which is produced upon major stress in terms of FC, the biologically active agent. Our study raises doubts regarding the accuracy of the TC measurement basally and after ACTH testing for diagnosing relative adrenal insufficiency in patients undergoing severe stress. However, whether this more pronounced increase is of physiopathological relevance remains to be seen. Surgery in our study was taken as the prototype stimulus for stress because it can readily be assessed experimentally. By extrapolation, this may include other forms of stress (6). Of course, coronary artery bypass grafting as an acute stress is not necessarily equivalent to the more chronic forms of stress in critical illness or sepsis. Nevertheless, if our findings were to be confirmed in a cohort of patients with severe sepsis, some patients could be wrongly diagnosed in terms of their adrenal reserve based on ACTH testing. The concept of relative adrenal insufficiency in such patients has already been challenged (6, 23, 24, 25).

In the original studies on the use of a pharmacological test of cortisol reserve, using insulin-induced hypoglycemia as a surrogate for responsivity to surgical stress, it was shown that the peak cortisol response to insulin could be used to predict those patients who might have a subnormal cortisol response to surgical stress (26, 27, 28, 29). Because the lowest level of cortisol seen in any patient undergoing major surgery was more than 20 µg /dl (~550 nmol/liter), patients showing this level of cortisol in response to insulin-induced hypoglycemia were assumed not to require corticosteroid cover during surgery. More recently, many groups have used pharmacological stimulation with synthetic ACTH as a more convenient surrogate for the insulin test (30, 31, 32). In the present study, as in many previous ones, the ACTH test using 250 µg synthetic ACTH showed similar peak levels of TC to ACTH and surgery, so it could be assumed that patients also showing such a response to synthetic ACTH will respond adequately to surgery with identical levels. However, the current data suggest that in terms of the biologically active FC, ACTH stimulation may not translate to surgical responsivity, and it sheds doubt as to the clinical validity of this test in our cohort. Additional studies assessing serum FC responses to insulin-induced hypoglycemia will be of considerable interest. However, although the insulin-induced hypoglycemia test may be considered the gold standard in the assessment of adrenal function, it is impractical and unsafe in the setting of acute stress such as major surgery (6).

CBG has a low capacity and high affinity, whereas albumin has a high capacity and low affinity for binding cortisol (6). Hypoalbuminemia is defined as a serum albumin concentration of 25 mg/liter or lower. A steady decrease in the percent bound cortisol is noted when albumin concentrations in plasma were less than 20 mg/liter (33). In our surgical patients with major stress, 70% of the patients had a serum albumin concentration below this threshold value. Accordingly, the calculated FC index increased by 130% compared with an almost 400% increase in FC, underlining that not only variations in CBG but also in serum albumin concentrations may have a major impact on FC and should not be neglected in the management of surgical patients with major stress. In this context, it is not surprising that FC levels showed a good albeit not perfect correlation with the calculated FC index in our study. The etiology of hypoalbuminemia in surgery and especially cardiac bypass surgery is complex and undoubtedly involves a dilution factor (34). This albumin lowering is caused in a large part by the volume of iv fluids used and blood loss (35), in addition to other potential mechanisms including increased capillary leakage, and altered intravascular and tissue albumin distribution (36, 37). Thus, it could be argued that this surgical procedure cannot be used as a surrogate stress for evaluating cortisol levels. As a limitation of our study, we did not assess the exact amount of fluid administration and blood loss. However, this dilution is not a unique finding to cardiac bypass surgery but is also seen to a similar extent in abdominal surgery (35) or sepsis (38). In addition, despite dilutional effects on circulating proteins, a coronary artery bypass procedure produces an acute-phase reaction of the same magnitude as sepsis, major trauma, and burns (39, 40).

Our newly developed assay to measure FC has certain advantages over other commercially available assays. First, equilibrium dialysis is generally seen as a reference method for measuring FC because no bound cortisol can be measured by virtue of the dialysis membrane. Second, the cost of setting up our assay is only a fraction of existing methods to measure FC (41, 42, 43). In addition, as noted above, alternative methods to calculate FC (e.g. FC index and Coolen’s equation) do not take into account all of the proteins to which cortisol can potentially bind. A simpler, less time-consuming alternative might be the assessment of salivary cortisol as it has been proposed as a valuable measure of FC (44, 45). Indeed, preliminary data suggest the usefulness of salivary cortisol in critical illness (46, 47).

As parameters of the systemic inflammatory response, we measured C-reactive protein and procalcitonin in our surgical patients. Both showed a significant increase with surgery and a significant correlation with TC and FC levels. The interactions between inflammatory cytokines and related peptides are complex, with evidence that such cytokines may act directly on the hypothalamus to increase the secretion of CRH and vasopressin, on the pituitary to stimulate ACTH release, and even directly on the adrenal via an ACTH-independent process (48, 49).

In conclusion, based on our data, FC concentrations measured with a newly developed assay provide a more accurate reflection of circulating glucocorticoids than TC levels. Our findings in support of this proposition are as follows: 1) with major stress, FC, but not TC, levels increase to a greater extent than after pharmacological ACTH testing; 2) basal FC levels were severalfold more elevated than TC levels after extubation; and 3) after resolution of major stress, basal FC levels fell promptly, but TC levels remained significantly more elevated. Our results also raise doubts as to the utility of some pharmacological tests of HPA reserve.


   Acknowledgments
 
We thank Jürg Girard, the staff of the Clinic of Endocrinology and Cardiothoracic Surgery (Head H. R. Zerkowski), the Departments of Medicine (Head J. A. Schifferli and A. P. Perruchoud), and the Department of Clinical Chemistry (P. Huber, C. Nusbaumer) of the University Hospital Basel for most helpful support during the study and the laboratory staff of the Barts Hospital London for help with the analysis.


   Footnotes
 
This work was supported by grants from the Swiss Foundation of Medical and Biological Stipends (SSMBS, PASMA-114617/1 to M.C.-C.).

Disclosure Statement: M.C.-C., S.J., I.W., O.C., C.K., H.P., J.P., R.E., B.M., and A.B.G. have nothing to declare.

First Published Online March 6, 2007

1 M.C.-C. and S.J. should be considered as contributing equally to this study. Back

Abbreviations: CBG, Corticosteroid-binding protein; FC, free cortisol; HPA, hypothalamo-pituitary-adrenal; NS, not significant; TC, total cortisol.

Received October 27, 2006.

Accepted February 26, 2007.


   References
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Discussion
 References
 

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M. Christ-Crain, D. Stolz, S. Jutla, O. Couppis, C. Muller, R. Bingisser, P. Schuetz, M. Tamm, R. Edwards, B. Muller, et al.
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