Free serum cortisol: quantification applying equilibrium dialysis or ultrafiltration and an automated immunoassay system

Highly Responsive Bioassay for Quantification of Glucocorticoids

Measurement of total cortisol levels in serum samples is currently based on immunoassays or liquid chromatography-mass spectrometry (LC-MS/MS). However, measurement of bioavailable cortisol is laborious, unreliable, and inconvenient for the patient. Therefore, a new versatile assay with the ability to measure both total and bioavailable cortisol from serum represents an important supplement to the current methods. We have generated a cell-based glucocorticoid reporter assay (HEK293F-GRE). The assay was validated for cell line stability, accuracy by dilution, precision, repeatability, reproducibility, and specificity. Additionally, the assay was tested for measuring both total and bioavailable cortisol in serum. The assay showed linearity at five dilution levels with R2 = 0.98 and an accuracy between 0.8 and 1.2. Precision (CV < 20%) was validated down to 3-6 nM dexamethasone, and estimation of the total cortisol concentration was comparable to cortisol immunoassay and LC-MS/MS in most serum samples. Moreover, the assay estimated the bioavailable cortisol fraction in serum samples to a level that agreed with the literature. The HEK293F-GRE assay holds the potential to be a complementary method for estimating cortisol in clinical practice. The ability to quantify bioavailable cortisol directly from serum samples is alluring and provides an opportunity for monitored and personal dose regimens of exogenous glucocorticoids.

Corticosteroid-binding Globulin (SERPINA6) Establishes Postpubertal Sex Differences in Rat Adrenal Development

Encoded by SerpinA6, plasma corticosteroid-binding globulin (CBG) transports glucocorticoids and regulates their access to cells. We determined how CBG influences plasma corticosterone and adrenal development in rats during the pubertal to adult transition using CRISPR/cas9 to disrupt SerpinA6 gene expression. In the absence of CBG, total plasma corticosterone levels were ∼80% lower in adult rats of both sexes, with a greater absolute reduction in females than in males. Notably, free corticosterone and adrenocorticotropic hormone were comparable between all groups. Between 30 and 90 days of age, wild-type female rats showed increases in adrenal weight and the size of the corticosterone-producing region, the zona fasciculata (zf), in tandem with increases in plasma CBG and corticosterone concentrations, whereas no such changes were observed in males. This sex difference was lost in rats without CBG, such that adrenal growth and zf expansion were similar between sexes. The sex-specific effects of CBG on adrenal morphology were accompanied by remarkable changes in gene expression: ∼40% of the adrenal transcriptome was altered in females lacking CBG, whereas almost no effect was seen in males. Over half of the adrenal genes that normally exhibit sexually dimorphic expression after puberty were similarly expressed in males and females without CBG, including those responsible for cholesterol biosynthesis and mobilization, steroidogenesis, and growth. Rat adrenal SerpinA6 transcript levels were very low or undetectable. Thus, sex differences in adrenal growth, morphology and gene expression profiles that emerge during puberty in rats are dependent on concomitant increases in plasma CBG produced by the liver.

Role of sex hormone-binding globulin in the free hormone hypothesis and the relevance of free testosterone in androgen physiology

According to the free hormone hypothesis, biological activity of a certain hormone is best reflected by free rather than total hormone concentrations. A crucial element in this theory is the presence of binding proteins, which function as gatekeepers for steroid action. For testosterone, tissue exposure is governed by a delicate equilibrium between free and total testosterone which is determined through interaction with the binding proteins sex hormone-binding globulin and albumin. Ageing, genetics and various pathological conditions influence this equilibrium, hereby possibly modulating hormonal exposure to the target tissues. Despite ongoing controversy on the subject, strong evidence from recent in vitro, in vivo and human experiments emphasizes the relevance of free testosterone. Currently, however, clinical possibilities for free hormone diagnostics are limited. Direct immunoassays are inaccurate, while gold standard liquid chromatography with tandem mass spectrometry (LC-MS/MS) coupled equilibrium dialysis is not available for clinical routine. Calculation models for free testosterone, despite intrinsic limitations, provide a suitable alternative, of which the Vermeulen calculator is currently the preferred method. Calculated free testosterone is indeed associated with bone health, frailty and other clinical endpoints. Moreover, the added value of free testosterone in the clinical diagnosis of male hypogonadism is clearly evident. In suspected hypogonadal men in whom borderline low total testosterone and/or altered sex hormone-binding globulin levels are detected, the determination of free testosterone avoids under- and overdiagnosis, facilitating adequate prescription of hormonal replacement therapy. As such, free testosterone should be integrated as a standard biochemical parameter, on top of total testosterone, in the diagnostic workflow of male hypogonadism.

Clinical and Technical Aspects in Free Cortisol Measurement

Accurate measurement of cortisol is critical in adrenal insufficiency as it reduces the risk associated with misdiagnosis and supports the optimization of stress dose. Comprehensive assays have been developed to determine the levels of bioactive free cortisol and their clinical and analytical efficacies have been extensively discussed because the level of total cortisol is affected by changes in the structure or circulating levels of corticoid-binding globulin and albumin, which are the main reservoirs of cortisol in the human body. Antibody-based immunoassays are routinely used in clinical laboratories; however, the lack of molecular specificity in cortisol assessment limits their applicability to characterize adrenocortical function. Improved specificity and sensitivity can be achieved by mass spectrometry coupled with chromatographic separation methods, which is a cutting-edge technology to measure individual as well as a panel of steroids in a single analytical run. The purpose of this review is to introduce recent advances in free cortisol measurement from the perspectives of clinical specimens and issues associated with prospective analytical technologies.

The Effect of High-Intensity Exercise on Changes in Salivary and Serum Cortisol Proportion Dynamics

Typically, salivary cortisol is reported as 5–10% of total cortisol, but the stability of this proportion and the effect of exercise on the 24-h profile is unclear. Therefore, this study investigated the circadian rhythm of the proportion of serum cortisol represented by salivary cortisol, and the impact of acute high-intensity exercise. Recreationally trained males (n = 8, age = 25.7 ± 2.4 years, height = 174.7 ± 7.8 cm, mass = 69.8 ± 12.1 kg) completed two 24-h profiles (rest and exercise conditions) for serum (Q60) and salivary (Q120) cortisol. Exercise consisted of 5 × 30 s sprinting intervals on the cycle ergometer. Cortisol was assessed using commercially available assays. The proportion (Cprop) of serum cortisol (Cser) represented by salivary cortisol (Csal) was calculated as [Cprop = Csal/ Cser × 100]. Multilevel growth models tested for trends across the 24-h profile. The highest relation between Cser and Csal was observed at 08:00 AM (r = 0.90). The average Cprop was 5.95% and demonstrated a circadian profile characterized by a cubic model. Acute exercise did not alter Cser, Csal, or Cprop. Thus, the proportion of Cser represented by Csal changes across a 24-h period and should be accounted for if using salivary cortisol to reflect circadian output of cortisol.

Glucocorticoid metabolism in critically ill dogs (Canis lupus familiaris)

Critical illness due to sepsis is a major global health concern associated with a high burden of mortality and cost. Glucocorticoid dysregulation in human sepsis is associated with poorer outcomes. This study examines glucocorticoid metabolism in septic canine patients to delineate elements of cellular dysregulation in common with critically ill humans and explore potential differences. This was a prospective case-control study conducted in the veterinary specialist critical care departments of two University teaching hospitals. Critically ill canine patients with naturally occurring sepsis or septic shock were compared with an in-hospital control population. Serum total, bound, and free cortisol concentrations were increased in septic shock (P < 0.001), and higher bound cortisol was associated with nonsurvival (P = 0.026). Urinary Gas Chromatography-Tandem Mass Spectrometry was performed to assess urinary glucocorticoid metabolites and estimate intracellular glucocorticoid metabolism. Decreased renal 11β-hydroxysteroid dehydrogenase 2 (11βHSD2) activity inferred from increased urinary cortisol-to-cortisone ratio was observed in critically ill dogs (P < 0.001). Decreased 11βHSD2 activity (P = 0.019) and increased A-ring reduction of cortisone (P = 0.001) were associated with nonsurvival within the critically ill dogs. Intriguingly, two dogs were identified with low circulating total cortisol (<2 mg/dL) associated with increased A-ring reduction of cortisol, not previously described. Investigation of spontaneous canine sepsis and septic shock reveals dysregulation of cortisol to cortisone conversion similar to that observed in human patients, but with differences in A-ring reduction compared with those reported in humans. In addition, two dogs with high levels of cortisol inactivation associated with low circulating cortisol concentrations were identified.

The plasma protein binding of the endogenous glucocorticosteroids is of vital importance for the concentrations in hair and saliva

BACKGROUND

The endogenous glucocorticosteroid cortisol (F) and its metabolite cortisone (E) are known to be involved in stress adaption and anti-inflammatory and immune regulatory effects. The ratios of F to E in the matrices serum, hair and saliva are different. The shift of this ratio by the enzyme activity of 11β-hydroxysteroid-dehydrogenase, which inactivates cortisol, was often discussed. The aim of our study was to calculate the contribution of the plasma protein binding (PPB) to this shift. The PPB of F is known to be 96% of the total F-Concentration in serum. The PPB of E was not analyzed in previous studies.

METHODS

Our study was designed to evaluate the correlation of corticosteroid concentrations in serum (total and free), hair and saliva. The samples were self-collected by the author (A.K.) monthly over a pregnancy cycle (1st samples before pregnancy, 8 samples during pregnancy and 5 samples postpartum). Serum protein binding was calculated from the determination of the total hormone concentrations of F and E (protein bound and unbound) and the free hormone concentrations in serum. The samples were processed by ether extraction and ultrafiltration. Hair samples were extracted with methanol and purified by solid-phase extraction. Saliva samples were collected using Salivette^® collection system. The concentrations of F and E were measured by liquid chromatography-mass spectrometry with LODs for free serum, total serum, hair and saliva of F: 0.11ng/mL, 2.13ng/mL, 1.6pg/mg, 0.08ng/mL and E: 0.12ng/mL, 0.54ng/mL, 2.1pg/mg, 0.09ng/mL, respectively.

RESULTS AND DISCUSSION

The serum concentrations (free and total) of both glucocorticosteroids rise up continuously during the time of pregnancy and decrease after delivery. The free and total serum concentrations were well correlated. No change was detected for the intensity of PPB of F. In contrast, the PPB of E decreases from 86.3% to 80.7% during pregnancy. The concentration ratios of F to E change from 3:1 in total serum to 1:1 in free serum. For hair samples, an increase of F and E in proximal segments was confirmed with the highest concentration 6.5weeks postpartum. Independently, corticosteroid concentrations in corresponding hair segments were found to be reduced with increasing distance from the root; an average decline of F and E by half in 5 and 6months was estimated, respectively. The counter effect of the mechanisms incorporation and wash-out is clearly visible. For saliva samples a good correlation with free, non-protein bound serum concentration was detected.

The role of corticosteroid-binding globulin in the evaluation of adrenal insufficiency

Cortisol is a hydrophobic molecule that is largely bound to corticosteroid-binding globulin (CBG) in the circulation. In the assessment of adrenal insufficiency, many clinicians measure a total serum cortisol level, which assumes that CBG is present in normal concentrations and with a normal binding affinity for cortisol. CBG concentration and affinity are affected by a number of common factors including oral contraceptive pills (OCPs), fever and infection, as well as rare mutations in the serine protease inhibitor A6 (SERPINA6) gene, and as such, total cortisol levels might not be the ideal way to assess adrenal function in all clinical circumstances. This paper reviews the limitations of immunoassay and liquid chromatography-tandem mass spectrometry (LC-MS/MS) in the measurement of total cortisol, the challenges of measuring free serum cortisol directly as well as the difficulties in calculating an estimated free cortisol from total cortisol, CBG and albumin concentrations. Newer approaches to the evaluation of adrenal insufficiency, including the measurement of cortisol and cortisone in the saliva, are discussed and a possible future role for these tests is proposed.

Population Pharmacokinetics of Prednisolone in Relation to Clinical Outcome in Children With Nephrotic Syndrome

BACKGROUND

The relapse frequency in children with nephrotic syndrome (NS) is highly variable despite standardized prednisolone treatment regimens. Existing evidence on the relationship between prednisolone pharmacokinetics (PK) and clinical response in children with NS is scarce and limited. The aim of this study was to develop a pediatric popPK model for prednisolone based on our previous model based on healthy adults using salivary measurements in children with NS and to correlate clinical outcome with between-subject variability in prednisolone exposure.

METHODS

The pharmacokinetics of prednisolone in a well-defined, prospective cohort consisting of 104 children with NS while in remission was determined. Pharmacokinetic parameters were analyzed in relation to relapse patterns and side effects. Noninvasive salivary prednisolone measurements were performed using a sparse sampling strategy. A population pharmacokinetic approach was used to derive individual estimates of apparent clearance (CL/F) and apparent volume of distribution (V/F) from the salivary concentration-time curve, followed by calculation of the area under the curve (AUC) of free prednisolone. The individual free serum prednisolone exposure from prednisolone in saliva was derived from the salivary concentration-time curves. Genetic polymorphisms of CYP3A4, CYP3A5, ABCB1, NR1L2, and POR were explored in relation to between-subject variability of CL/F.

RESULTS

Moderate interindividual variability was found for CL/F (CV, 44.7%). Unexplained random between-subject variability (eta) of CL/F was lower in patients carrying 1 or 2 ABCB1 3435C>T alleles compared to wild type: median -0.04 (interquartile range, -0.17 to 0.21) and 0.00 (-0.11 to 0.16) versus 0.17 (-0.08 to 0.47), P = 0.046. Exposure to free prednisolone was not associated with frequent relapses or adverse effects.

CONCLUSIONS

This study provides evidence for the possibility of prednisolone drug monitoring through salivary measurements and this may be of particular usefulness in pediatric patients. However, the observed variability in prednisolone exposure, in the therapeutic dose range studied, is not considered to be a major determinant of clinical outcome in children with NS.

Three calculations of free cortisol versus measured values in the critically ill

OBJECTIVES

To investigate the agreement between the calculated free cortisol levels according to widely applied Coolens and adjusted Södergård equations with measured levels in the critically ill.

DESIGN AND METHODS

A prospective study in a mixed intensive care unit. We consecutively included 103 patients with treatment-insensitive hypotension in whom an adrenocorticotropic hormone (ACTH) test (250μg) was performed. Serum total and free cortisol (equilibrium dialysis), corticosteroid-binding globulin and albumin were assessed. Free cortisol was estimated by the Coolens method (C) and two adjusted Södergård (S1 and S2) equations. Bland Altman plots were made.

RESULTS

The bias for absolute (t=0, 30 and 60min after ACTH injection) cortisol levels was 38, -24, 41nmol/L when the C, S1 and S2 equations were used, with 95% limits of agreement between -65-142, -182-135, and -57-139nmol/L and percentage errors of 66, 85, and 64%, respectively. Bias for delta (peak-baseline) cortisol was 14, -31 and 16nmol/L, with 95% limits of agreement between -80-108, -157-95, and -74-105nmol/L, and percentage errors of 107, 114, and 100% for C, S1 and S2 equations, respectively.

CONCLUSIONS

Calculated free cortisol levels have too high bias and imprecision to allow for acceptable use in the critically ill.

A practical limited sampling strategy to predict free prednisolone exposure and glycemia in kidney transplant recipients

BACKGROUND

Despite significant interindividual variability in prednisolone pharmacokinetics and potentially serious consequences with inadequate or excessive exposure, monitoring of prednisolone levels is not employed to guide therapy. As ultrahigh-performance liquid chromatography-tandem mass spectrometry methods can now measure the active free fraction of prednisolone, this study aimed to evaluate the performance of 15 published limited sampling strategies (LSSs) for predicting free prednisolone exposure in adult kidney transplant recipients and to examine the relationship between free/total prednisolone exposure and plasma glucose.

METHODS

The study was performed in 11 subjects without diabetes 3-4 weeks postkidney transplantation. Area under the concentration time curve profiles of total and free prednisolone from 0 to 12 hours postdose (AUC₀₋₁₂) were determined and compared with predicted AUC₀₋₁₂ values calculated from published LSSs. Venous glucose was measured concurrently with the 13 sampling time points.

RESULTS

The mean (±SD) age of subjects was 52 ± 12 years, 5 were men and the median (interquartile range) daily prednisolone dose was 20.0 mg (20.0-22.5). Interindividual variation in dose-adjusted free and total prednisolone exposure was 1.9- and 3.2-fold, respectively. All 15 free prednisolone LSSs exhibited good correlation (r ≥ 0.83), with bias and imprecision less than 15%. An LSS incorporating 1.25- and 3-hour samples had the highest predictive power (r = 0.97, bias 1.2%, imprecision 5.6%). Free prednisolone AUC₀₋₁₂ correlated with peak glucose levels (r = 0.65, P = 0.037), as did predicted AUC₀₋₁₂ from 14/15 LSSs.

CONCLUSIONS

Biologically active free prednisolone exposure can be accurately predicted postkidney transplantation by LSSs incorporating 2-point concentration sampling. Peak plasma glucose concentration correlated well with prednisolone exposure.

Regulation of cortisol bioavailability--effects on hormone measurement and action

Routine assessment of the hypothalamic-pituitary-adrenal axis relies on the measurement of total serum cortisol levels. However, most cortisol in serum is bound to corticosteroid-binding globulin (CBG) and albumin, and changes in the structure or circulating levels of binding proteins markedly affect measured total serum cortisol levels. Furthermore, high-affinity binding to CBG is predicted to affect the availability of cortisol for the glucocorticoid receptor. CBG is a substrate for activated neutrophil elastase, which cleaves the binding protein and results in the release of cortisol at sites of inflammation, enhancing its tissue-specific anti-inflammatory effects. Further tissue-specific modulation of cortisol availability is conferred by corticosteroid 11β-dehydrogenase. Direct assessment of tissue levels of bioavailable cortisol is not clinically practicable and measurement of total serum cortisol levels is of limited value in clinical conditions that alter prereceptor glucocorticoid bioavailability. Bioavailable cortisol can, however, be measured indirectly at systemic, extracellular tissue and cell levels, using novel techniques that have provided new insight into the transport, metabolism and biological action of glucocorticoids. A more physiologically informative approach is, therefore, now possible in the assessment of the hypothalamic-pituitary-adrenal axis, which could prove useful in clinical practice.

[Perioperative Addisonian crisis]

An Addisonian crisis marks an acute adrenocortical failure which can be caused by decompensation of a chronic insufficiency due to stress, an infarct or bleeding of the adrenal cortex and also abrupt termination of a long-term glucocorticoid medication. This article reports the case of a 25-year-old patient with Crohn's disease who suffered an Addisonian crisis with hypotension, hyponatriemia and hypoglycemia during an emergency laparotomy after he had terminated prednisolone medication on his own authority. This necessitated an aggressive volume therapy in addition to an initial therapy with 100 mg hydrocortisone, 8 g glucose and a continuous administration of catecholamines. Under this treatment regimen hemodynamic stabilization was achieved. Reduction of the administration of hydrocortisone after 3 days resulted in cardiovascular insufficiency which required an escalation of the hydrocortisone substitution.

Challenges for the endocrine laboratory in critical illness

The endocrine laboratory must provide accurate and timely results for the critically ill patient. A number of pathophysiological factors affect assay systems for adrenal, thyroid and gonadal function tests. The effects are primarily on estimates of 'free hormone' concentration through abnormal binding protein concentrations and the effects of drugs and metabolites on hormone-protein binding. The limitations of the principal analytical techniques (immunoassay and chromatography-mass spectrometry) include drug effects, endogenous antibody interference and ion suppression. These effects are not always easily identified. Analytical specificity and standardisation result in differences in bias between assays and thus a requirement for assay specific decision limits and reference ranges. Good communication between clinician and laboratory is needed to minimise these effects. Developments in mass spectrometry should lead to greater sensitivity and wider applicability of the technique. International efforts to develop higher order reference materials and reference method procedures should lead to greater comparability of results.

Real-time free cortisol quantification among critically ill children

OBJECTIVES

Ascertainment of adrenal function assessing free rather that total cortisol may be beneficial for the diagnosis of critical illness-related cortisol insufficiency. We hypothesized that centrifugal ultrafiltration would provide timely free cortisol data that highly correlated with the gold standard, but logistically cumbersome, equilibrium dialysis technique when the free cortisol fractions were identically quantified by chemiluminescence immunoassay. We also hypothesized that free cortisol would correlate with illness severity in a large cohort of critically ill children.

DESIGN

Prospective, multi-institutional, observational cohort investigation.

SETTING

Seven pediatric intensive care units within the Eunice Kennedy Shriver National Institute of Child Health and Human Development Collaborative Pediatric Critical Care Research Network.

PATIENTS

One hundred sixty-five critically ill children across the spectrum of illness severity.

INTERVENTIONS

Blood sampling.

MEASUREMENTS AND MAIN RESULTS

Time to derive plasma free cortisol concentrations after centrifugal ultrafiltration or equilibrium dialysis fractionation with chemiluminescence immunoassay was approximately 2 vs. approximately 24 hrs, respectively. Using centrifugal ultrafiltration, mean plasma free cortisol was 4.1 ± 6.7 μg/dL (median, 1.6 μg/dL; range, 0.2-43.6 μg/L), representing an average of 15.2 ± 9.4% of total cortisol. Nearly 60% of subjects exhibited free cortisol <2 and 30% <0.8 μg/dL, previously suggested threshold concentrations for defining critical illness-related cortisol insufficiency. Plasma-free cortisol concentrations comparing centrifugal ultrafiltration vs. equilibrium dialysis fractionation demonstrated a strong correlation (R2 = 0.97). For free cortisol <2 μg/dL, Bland-Altman analysis revealed minimal negative bias for the centrifugal ultrafiltration technique. Illness severity assessed by Pediatric Risk of Mortality III correlated moderately with free cortisol and percent total cortisol as free cortisol.

CONCLUSIONS

Determination of centrifugal ultrafiltration fractionated free cortisol was fast and results correlated highly with equilibrium dialysis fractionated free cortisol. Many children exhibited free cortisol <2 and <0.8 μg/dL but did not demonstrate clinical evidence of critical illness-related cortisol insufficiency. This study ascertains that real-time free cortisol quantification is feasible to potentially help guide clinical decision-making for cortisol replacement therapy in the pediatric intensive care unit.

Assessing adrenal insufficiency of corticosteroid secretion using free versus total cortisol levels in critical illness

PURPOSE

To study the value of free versus total cortisol levels in assessing relative adrenal insufficiency during critical illness-related corticosteroid insufficiency.

METHODS

A prospective study in a mixed intensive care unit from 2004 to 2007. We consecutively included 49 septic and 63 non-septic patients with treatment-insensitive hypotension in whom an adrenocorticotropic hormone (ACTH) test (250 μg) was performed. Serum total and free cortisol (equilibrium dialysis), corticosteroid-binding globulin (CBG) and albumin were assessed.

RESULTS

Although a low CBG resulted in a high free cortisol level relative to total cortisol, free and total cortisol and their increases were well correlated (r = 0.77-0.79, P < 0.001). In sepsis, hypoalbuminemia did not affect total and free cortisol, and increases in total cortisol upon ACTH predicted increases in free cortisol regardless of low binding proteins. In non-sepsis, total cortisol was lower with than without hypoalbuminemia; free cortisol did not differ, since hypoalbuminemia concurred with a low CBG. Increases in total cortisol depended less on binding proteins than on raw levels. The areas under the receiver operating characteristic curve for predicting increases in free from total cortisol were 0.93-0.97 in sepsis and 0.79-0.85 in non-sepsis (P = 0.044 or lower for sepsis vs. non-sepsis).

CONCLUSIONS

Although the biologically active free cortisol fraction depends on binding proteins, total cortisol correlates to free cortisol in treatment-insensitive hypotension during critical illness. In sepsis, albumin is not an important binding molecule. Subnormal increments in total cortisol upon ACTH suffice in assessing relative adrenal insufficiency, particularly in sepsis.

Serum regulates cortisol bioactivity by corticosteroid-binding globulin-dependent and independent mechanisms, as revealed by combined bioassay and physicochemical assay approaches

CONTEXT

Corticosteroid-binding globulin (CBG) is the principal carrier of natural glucocorticoids in the circulation, and we hypothesized that it modulates glucocorticoid bioactivity (GBA). Alterations in CBG, the presence of noncortisol, naturally occurring glucocorticoids and the use of potent, synthetic glucocorticoids, all make it difficult to assess adrenal activity in-vivo; these problems can be addressed by a glucocorticoid bioassay.

DESIGN AND SUBJECTS

A bioassay was developed for serum GBA and a physicochemical ultrafiltration-liquid chromatography-tandem mass spectrometry assay for free serum cortisol (FreeF). We studied individuals homozygous and heterozygous for a nonfunctioning CBG variant (CBG G237V) and healthy controls.

RESULTS

FreeF concentrations were similar in healthy controls, and those with absent functional CBG, but surprisingly we found low GBA in CBG null individuals. This may suggest that CBG delivers cortisol to target cells. However, further experiments revealed that dilution of serum in the bioassay caused release of cortisol from CBG, resulting in elevated GBA measurements in all but the CBG G237V homozygotes. Furthermore, we identified a specific and potent inhibitory effect of high concentration serum on glucocorticoid sensitivity of the recipient cells used in the bioassay. Analysis of inflammatory synovial fluid, a filtrate of serum with lower CBG concentration, revealed elevated free cortisol compared to noninflammatory synovial fluid, a change not attributable to interconversion between cortisol and cortisone.

CONCLUSIONS

Our findings reveal that dilution of CBG enhances cortisol release, and so bioactivity, and also that serum potently induces glucocorticoid resistance in target cells.

Initial observations regarding free cortisol quantification logistics among critically ill children

PURPOSE

Corticosteroid insufficiency may occur among critically ill patients, but the diagnosis remains controversial. Historically assessment of free cortisol (FC) by means of equilibrium dialysis (ED) has required large blood volumes and prolonged fractionation time preceding analysis. We hypothesized that temperature-controlled centrifugal ultrafiltration with chemiluminescence immunoassay (CU/CI) would provide real-time FC data that highly correlated with ED/radioimmunoassay (ED/RI) or liquid chromatography/mass spectrometry (LC/MS) techniques.

METHODS

We quantified and correlated baseline and corticotropin-stimulated TC and FC by means of CU/CI, ED/RI, and LC/MS among healthy adults and 37 critically ill children.

RESULTS

Among critically ill children, FC was three- to fivefold higher than the healthy adults at baseline and increased another five- to eightfold following corticotropin administration. While TC increased approximately twofold following corticotropin administration, FC increased on average more than eightfold. Serum FC per CU/CI highly correlated with FC per ED/RI or LC/MS, but results were available in a fraction of the time. Children failing to increase TC by >9.0 μg/dL (248 nM) following corticotropin demonstrated an appropriate FC increase. Nearly 50% of critically ill children exhibited FC <2.0 μg/dL (55 nM). Neither FC nor TC concentrations correlated significantly with measures of illness severity.

CONCLUSIONS

Quantification of FC utilizing CU/CI was fast (1-2 h) and results correlated highly with ED/RI or LC/MS methodologies. These data require validation with larger cohorts of healthy and critically ill children but indicate that real-time FC quantification is available to guide cortisol replacement therapy.

Dithiobis(succinimidyl propionate) modified gold microarray electrode based electrochemical immunosensor for ultrasensitive detection of cortisol

Gold microelectrode arrays functionalized with dithiobis(succinimidyl propionate) self-assembled monolayer (SAM) have been used to fabricate an ultrasensitive, disposable, electrochemical cortisol immunosensor. Cortisol specific monoclonal antibody (C-Mab) was covalently immobilized on the surface of gold microelectrode array and the sensors were exposed to solutions with different cortisol concentration. After C-Mab binding, unreacted active groups of DTSP were blocked using ethanol amine (EA) and label-free electrochemical impedance (EIS) technique was used to determine cortisol concentration. EIS results confirmed that EA/C-Mab/DTSP/Au based biosensor can accurately detect cortisol in the range of 1pM-100nM. The biosensor was successfully used for the measurement of cortisol in interstitial fluid in vitro. This research establishes the feasibility of using impedance based biosensor architecture for disposable, wearable cortisol detector.

An evaluation of measured and calculated serum free cortisol in a group of patients with known adrenal suppression

Background

Since more than 90% of cortisol is bound to protein, serum free cortisol (SFC) may be a more appropriate marker of adrenal status than total cortisol. However, measurement of SFC is technically difficult and calculated SFC may offer a more practical alternative.

Methods

SFC, measured by equilibrium dialysis coupled with immunoassay, and calculated using Coolens' equation from total cortisol and corticosteroid binding globulin (CBG) concentrations, was compared in short Synacthen test (SST) serum from 42 patients, of whom 20 demonstrated a suppressed adrenal response.

Results

Considering the patient group as a whole, calculated SFC was found to be significantly lower than measured SFC, pre- and post-Synacthen ( P < 0.05 and <0.001, respectively). Upon classifying the patients as pass or fail based on total cortisol response to Synacthen, the difference in calculated and measured SFC only reached statistical significance for post-Synacthen concentrations in the pass group ( P < 0.01), suggesting a greater discrepancy at higher cortisol concentrations. There was no difference in CBG levels between the pass and fail groups and both measured and calculated SFC gave a diminished 30 min response in subjects deemed to have failed the SST.

Conclusion

Coolens' equation was found to underestimate measured SFC in this cohort of outpatients, as has been previously demonstrated, particularly in patients with a pronounced acute phase response. Although calculated SFC gave a diminished response in individuals deemed to have failed the SST, the concentration-dependent nature of the discrepancy may limit the usefulness of this method for assessing adrenal status.

Steroid assays in paediatric endocrinology

Most steroid disorders of the adrenal cortex come to clinical attention in childhood and in order to investigate these problems, there are many challenges to the laboratory which need to be appreciated to a certain extent by clinicians. The analysis of sex steroids in biological fluids from neonates, over adrenarche and puberty present challenges of specificities and concentrations often in small sample sizes. Different reference ranges are also needed for interpretations. For around 40 years, quantitative assays for the steroids and their regulatory peptide hormones have been possible using immunoassay techniques. Problems are recognised and this review aims to summarise the benefits and failings of immunoassays and introduce where tandem mass spectrometry is anticipated to meet the clinical needs for steroid analysis in paediatric endocrine investigations. It is important to keep a dialogue between clinicians and the laboratory, especially when any laboratory result does not make sense in the clinical investigation.

Serum macrophage migration inhibitory factor reflects adrenal function in the hypothalamo-pituitary-adrenal axis of septic patients: an observational study

Background

The hypothalamo-pituitary-adrenal (HPA) axis modulates the inflammatory response during sepsis. Macrophage migration inhibitory factor (MIF), which counteracts the anti-inflammatory activity of glucocorticoid (GC), is one of the mediators of the development of inflammation. An inflammatory imbalance involving GC and MIF might be the cause or result of adrenal insufficiency. Our objective was to clarify the relationship between serum MIF and adrenal function in the HPA axis of sepsis patients using the adrenocorticotropic hormone (ACTH) stimulation test.

Methods

An observational study was performed in a university intensive care unit over a two-year period. Of 64 consecutive sepsis patients, 41 were enrolled. The enrolled patients underwent an ACTH stimulation test within 24 h of the diagnosis of severe sepsis or septic shock. Clinical and laboratory parameters, including serum MIF and cortisol, were measured.

Results

Based on their responses to the ACTH stimulation test, the patients were divided into a normal adrenal response (NAR) group (n = 22) and an adrenal insufficiency (AI) group (n = 19). The AI group had significantly more septic shock patients and higher prothrombin time ratios, serum MIF, and baseline cortisol than did the NAR group (P < 0.05). Serum MIF correlated significantly with the SOFA (Sequential Organ Failure Assessment) score, prothrombin time ratio, and delta max cortisol, which is maximum increment of serum cortisol concentration after ACTH stimulation test (rs = 0.414, 0.355, and -0.49, respectively, P < 0.05). Serum MIF also correlated significantly with the delta max cortisol/albumin ratio (rs = -0.501, P = 0.001). Receiver operating characteristic curve analysis identified the threshold serum MIF concentration (19.5 ng/mL, P = 0.01) that segregated patients into the NAR and AI groups.

Conclusions

The inverse correlation between serum MIF and delta max cortisol or the delta max cortisol/albumin ratio suggests that high serum MIF reflects an insufficient adrenal response in the HPA axis. Serum MIF could be a valuable clinical marker of adrenal insufficiency in sepsis patients.

[Corticosteroid insufficiency in the critically ill. Pathomechanisms and recommendations for diagnosis and treatment]

Critically ill patients with severe systemic inflammation can develop critical illness-related corticosteroid insufficiency (CIRCI), which is associated with a poor outcome. A task force of the American College of Critical Care Medicine compiled recommendations for diagnosis and treatment of this clinical entity thereby focusing on patients with septic shock and acute respiratory distress syndrome (ARDS). The results of large scale multi-centre trials gave partially conflicting results arguing against the broad use of corticosteroids in stress doses. However, the task force recommended treatment with stress-dose corticosteroids in patients with septic shock who respond poorly to fluid resuscitation and vasopressor therapy and in patients with early ARDS (<14 days after onset). The dose of corticosteroids should be reduced in a step-wise manner. Corticosteroids at stress doses are currently under investigation in other target populations of critically ill patients potentially suffering from CIRCI. Preliminary data suggest that patients with vasodilatory shock after cardiac surgery and patients with liver cirrhosis and sepsis can benefit from corticosteroids. Critical illness-related corticosteroid insufficiency can also occur in patients with trauma, traumatic brain injury, acute pancreatitis and burn injuries, but data from clinical trials on these target groups are insufficient at present. The therapeutic use of corticosteroids in stress doses reduces the incidence of post-traumatic stress disorder (PTSD) after intensive care treatment.

Cortisol assays and diagnostic laboratory procedures in human biological fluids

The overview of cortisol physiology, action and pathology is achieved in relation to the hypothalamic-pituitary-adrenal axis alteration by laboratory investigation. The measurements of cortisol and related compound levels in blood, urine and saliva used to study the physiological and pathological cortisol involvement, are critically reviewed. The immunoassay and chromatographic methods for cortisol measurement in the various biological fluids are examined in relation to their analytical performances, reference ranges and diagnostic specificity and sensitivity. Moreover, blood, urine and saliva cortisol level measurements are described taking into account the diagnostic implications. The deduction is that each method requires the definition of its own reference range and its related diagnostic cut-off levels. Thus, this review, stressing the analysis procedures, could help to understand and compare the results of the different assays.