Interference in ACTH immunoassay negatively impacts the management of subclinical hypercortisolism

Adrenocorticotropic Hormone Measured by Immulite 1000 and Elecsys Assay Platforms in Suspected Cases of Hypocortisolism: A Word of Caution

OBJECTIVE

Several reports suggested that adrenocorticotropic hormone (ACTH) level measured by Immulite 1000 may be falsely elevated leading to misdiagnosis of etiology of Cushing syndrome. However, when it comes to fallacies of ACTH measurement in suspected cases of hypocortisolism, evidence is limited. We explored the performance of ACTH assays using Immulite 1000 and Elecsys Cobas immunoassay platforms in subjects with hypocortisolism.

METHODS

In this observational, cross-sectional study, 104 patients with haemoglobin E/beta-thalassemia were subjected to 9 am serum cortisol, direct renin concentration, and plasma aldosterone. Plasma ACTH was measured in Immulite 1000 and Elecsys Cobas platforms. Both 1 μg and 250 μg Synacthen stimulation tests were performed to diagnose adrenal insufficiency.

RESULTS

Among 104 patients with haemoglobin E/beta-thalassemia, 34 had primary adrenal insufficiency, 9 had secondary adrenal insufficiency, and 33 had subclinical adrenal insufficiency. Mean plasma ACTH (n = 104) measured by Immulite 1000 and Elecsys was 83.42 ± 63.46 pg/mL versus 52.10 ± 38.14 pg/mL, respectively (P < .001). The values had good correlation (r = 0.341, P < .001); however, the agreement between measured values was not strong (Cohen's κ = 0.208, P = .001). With regard to the diagnosis of primary adrenal insufficiency, specificity of Immulite 1000 was low compared with Elecsys (27.86% vs 80.32%). Furthermore, 2 patients with secondary adrenal insufficiency had inappropriately elevated ACTH measured at Immulite 1000 assay platform.

CONCLUSION

Use of Immulite 1000 platform may result in falsely elevated ACTH values. Physicians should exercise caution while interpreting the results and repeat test using a different assay platform may be considered.

Detecting the interferences in adrenocorticotropic hormone measurement - three cases reinforcing the efficiency of the complementary clinical and laboratory audit

Accurate measurement of adrenocorticotropic hormone (ACTH) is crucial in the evaluation of pituitary and adrenal disorders. Although great progress has been achieved in ACTH measurement with immunometric assays, interference may occur and adversely affect the clinical management. The report contributes to compiling the evidence on the clinical challenges with the management of the interferences in the ACTH measurement by presenting three cases: two with clinically overt hypercortisolism and discrepant ACTH concentrations within the reference interval; the third case describes the falsely elevated ACTH in a patient with secondary adrenal insufficiency. In all patients, the results obtained with the two immunometric platforms, chemiluminescence (CLIA) immunoassay (Siemens, Immulite) and electrochemiluminescence (ECLIA) immunoassay (Roche, Cobas), were discordant. Serial dilution of plasma samples revealed nonlinearity. After polyethylene glycol (PEG) precipitation recoveries were less than 22%, 26%, and 3%, respectively, supporting interference. Moreover, a decrease in ACTH concentration after incubation in a heterophile antibody-blocking tube was observed in the second case. In the first case, misinterpretation of ACTH led to inferior petrosal sinus sampling (IPSS), whereas timely detection of assay interference prevented further investigations in other cases. Increasing awareness regarding ACTH interference and comprehensive approach in evaluation could allow timely detection, helping to prevent unnecessary testing and perplexing clinical outcomes.

Multiple immunoassay interference in a patient with falsely elevated calcitonin

Calcitonin (CT) is a diagnostic and follow-up marker of medullary thyroid carcinoma. Heterophile antibodies (HAbs) may interfere during immunometric assay measurements and result in falsely high CT levels and different markers. A 50-year-old female patient was referred to our institution for elevated CT levels (3,199 pg/mL [0-11,5]). Physical examination and thyroid ultrasonography show no thyroid nodules. Because of the discrepancy between the clinical picture and the laboratory results, various markers and hormones were examined to determine whether there was any interference in the immunometric assay. Thyroglobulin (Tg) and Adrenocorticotropic hormone (ACTH) levels were also found inaccurately elevated. After precipitation with polyethylene glycol, CT, Tg, and ACTH levels markedly decreased, showing macro-aggregates. Also, serial dilutions showed non-linearity in plasma concentrations. Additionally, CT samples were pretreated with a heterophilic blocking tube before measuring, and the CT level decreased to < 0.1 pg/mL, suggesting a HAb presence. Immunoassay interference should be considered when conflicting laboratory data are observed. This may help reduce the amount of unnecessary laboratory and imaging studies and prevent patients from complex diagnostic procedures.

Utilizing dehydroepiandrosterone sulfate and its ratio for detecting mild autonomous cortisol excess in patients with adrenal incidentaloma

Subclinical Cushing syndrome is a condition of mild autonomous cortisol excess (MACE) that lacks typical features of Cushing syndrome but is associated with many complications. It represents a common hormonal dysfunction among patients with adrenal incidentaloma (AI), defined as unexpected masses or lesions found in the adrenal glands during radiological examinations of the chest or abdomen unrelated to adrenal gland assessment. The study evaluated the accuracy of dehydroepiandrosterone sulfate (DHEA-S) and dehydroepiandrosterone sulfate ratio (calculated by dividing the DHEA-S value by the age and sex-adjusted normal range of DHEA-S) in detecting MACE in AI patients. A cross-sectional study was conducted from April 2021 to July 2022 at the Faiha Specialized Diabetes, Endocrine, and Metabolism Centre (FDEMC) in Basrah, southern Iraq, involving 38 AI patients. Comprehensive laboratory and radiological evaluations were performed, including tests for adrenocorticotropic hormone (ACTH), renin, aldosterone, aldosterone/renin ratio (ARR), metanephrine, normetanephrine, cortisol, DHEA-S, and the 1-mg overnight dexamethasone suppression test (1-mg ONDST). Among the AI patients, 14% had MACE. Both DHEA-S ≤75 µg/dL and a DHEA-S ratio ≤1.7 exhibited a sensitivity of 80% each, with specificities of 73.3% and 76.6%, respectively, in diagnosing MACE in individuals aged ≤65 years. The negative predictive values were 95.7% and 95.8%, respectively. Low DHEA-S and DHEA-S ratio had high sensitivity and specificity in predicting MACE among AI patients aged ≤65 years, with strong negative predictive value.

Intraoperative Predictor of Remission in Cushing Disease

BACKGROUND

Cushing disease represents a challenge for neurosurgeons, with high recurrence rates reported. Characteristics associated with remission are incompletely understood; thus, an intraoperative predictor for outcome would be valuable for assessing resection of adrenocorticotropic hormone (ACTH) secreting tissue.

OBJECTIVE

To evaluate whether intraoperative ACTH measurement could predict outcome after surgery for Cushing disease.

METHODS

Retrospective cohort study of 55 consecutive encounters with Cushing disease who had peripheral plasma ACTH levels measured intraoperatively before, during, and after tumor resection. The primary outcome measure was remission, defined by either 2 negative 24-hour urine free cortisol or 2 negative midnight salivary cortisol measurements. A logistic regression machine learning model was generated using recursive feature elimination.

RESULTS

Fifty-five operative encounters, comprising 49 unique patients, had a mean follow-up of 2.73 years (±2.11 years) and a median follow-up of 2.07 years. Remission was achieved in 69.1% (n = 38) of all operations and in 78.0% (n = 32) of those without cavernous sinus invasion. The final ACTH level measured intraoperatively correctly predicted outcome (area under the curve = 0.766; P value = .002). The odds ratio of remission in patients with the lowest quartile vs highest quartile final intraoperative ACTH was 23.4 ( P value = .002). Logistic regression machine learning model resulted in incorporating postoperative day 1 morning cortisol, final intraoperative ACTH that predicted outcome with an average area under the curve of 0.80 ( P = .0027).

CONCLUSION

Intraoperative ACTH may predict outcome after surgery in Cushing disease; furthermore, investigation is warranted.

Sensitivity of Different ACTH and Cortisol Concentration Values in Corticotropin-Releasing Hormone Based Tests in Cushing's Disease

PURPOSE

In Cushing's disease (CD) patients, the aim of the present study is to confirm sensitivity of several ACTH and cortisol concentration values in different time points, during corticotropin-releasing hormone (CRH) stimulation test and during CRH stimulation following dexamethasone suppression (DEX-CRH) test.

METHODS

We retrospectively analyzed cortisol and ACTH concentration increment during CRH and DEX-CRH tests in 23 patients with confirmed CD. Cortisol and ACTH concentrations were determined immediately before, 15 min and 30 min after CRH stimulation. We evaluated the sensitivity of different cutoff values including those reported in previous studies, in the diagnosis of CD.

RESULTS

During DEX-CRH test, 15 min serum cortisol concentration of 1.4 μg/dl (38 nmol/L) had a sensitivity of 90.9%, and serum cortisol concentration ≥1.27 μg/dl (35 nmol/L) had a sensitivity of 100%. For plasma ACTH, sensitivity of 100% was obtained using ACTH ≥3.5pmol/L (16 pg/ml) at 30 min. During CRH test, 35% increase from baseline in ACTH concentration had a sensitivity of 72.7%. Twenty percent increase in cortisol 30 minutes after stimulation yielded a sensitivity of 85.7%. The best sensitivity of ACTH and cortisol increment was obtained 15 min after stimulation, using 19% and 9% increase, respectively (sensitivity of 100% and 92.8%, respectively).

CONCLUSION

During CRH and DEX-CRH tests, the study findings agree with the good sensitivity of ACTH and cortisol cutoff values suggested in previous studies; yet, other cutoff values may give a higher diagnostic sensitivity.

Clinical Spectrum of Adrenal Cushing's Syndrome and the Caution for Interpretation of Adrenocorticotrophic Hormone: A Single-Center Experience

To describe the differences in presentation, biochemistry, and radiological evaluation of various etiologies of adrenal Cushing's syndrome (CS) from a single center. To emphasize caution for interpretation of plasma adrenocorticotropic hormone (ACTH), as a spuriously unsuppressed ACTH level by immunometric assay may lead to therapeutic misadventures in adrenal CS.

DESIGN

 Retrospective, single-center, observational study.

METHODS

  Fifty-eight adrenal CS patients [Adrenocortical carcinoma (ACC), n=30; Adenoma (ACA), n=15; Primary pigmented nodular adrenocortical disease (PPNAD), n=10; ACTH independent macronodular adrenal hyperplasia (AIMAH), n=3) evaluated at a tertiary care center in western India between January 2006 to March 2020 were included. Data on demography, clinical evaluation, biochemistry, imaging, management, histopathology, and outcome were recorded in a standard format and analyzed.

RESULTS

  Cortisol secreting ACC presented at 38(1-50) years with abdominal mass in 26/30 (86.7%) and 16/30 (53.3%) had metastases at presentation. ACA with autonomous cortisol excess presented at 25(4.9-40) years with discriminating features of CS in 14/15 (93.3%), sex steroid production in 2/15, unenhanced HU <10 in only one, and relative washout >40% in 8/11 (72.7%). One ACA and eight ACC patients had plasma ACTH (by Siemens Immulite assay) > 20 pg/ml, despite hypercortisolemic state.

CONCLUSIONS

  Cortisol-secreting ACC and ACA most often present with mass effects and florid CS, respectively. Baseline HU has low sensitivity to differentiate cortisol-secreting ACA from ACC. Plasma ACTH measured by Seimens Immulite is often unsuppressed, especially in ACC patients, which can be addressed by measuring ACTH by more accurate assays.

Proteoforms and their expanding role in laboratory medicine

The term “proteoforms” describes the range of different structures of a protein product of a single gene, including variations in amino acid sequence and post-translational modifications. This diversity in protein structure contributes to the biological complexity observed in living organisms. As the concentration of a particular proteoform may increase or decrease in abnormal physiological states, proteoforms have long been used in medicine as biomarkers of health and disease. Notably, the analytical approaches used to analyze proteoforms have evolved considerably over the years. While ligand binding methods continue to play a large role in proteoform measurement in the clinical laboratory, unanticipated or unknown post-translational modifications and sequence variants can upend even extensively tested and vetted assays that have successfully made it through the medical regulatory process. As an alternate approach, mass spectrometry—with its high molecular selectivity—has become an essential tool in detection, characterization, and quantification of proteoforms in biological fluids and tissues. This review explores the analytical techniques used for proteoform detection and quantification, with an emphasis on mass spectrometry and its various applications in clinical research and patient care including, revealing new biomarker targets, helping improve the design of contemporary ligand binding in vitro diagnostics, and as mass spectrometric laboratory developed tests used in routine patient care.

Consideration triggered by the choice of heterophilic antibody interference detection tests in measuring ACTH for a teenager boy with a rare adrenal disease

BACKGROUND

Plasma ACTH is an important marker for Cushing syndrome; inaccurate measurement of ACTH concentrations due to the serum heterophile antibody may mislead diagnosis by physicians. We describe the case of a teenage boy with a rare adrenal disease who presented falsely increased ACTH concentrations (20.3 pg/ml; Siemens Immulite).

METHODS

Low dose dexamethasone inhibition test showed no inhibition of serum cortisol. While biochemical evidence suggested ACTH-dependent Cushing, the imaging tests suggested otherwise. Hence, further tests for interference identification, including test platform replacement, sample dilution, PEG precipitation, and use of blocking antibodies, were conducted.

RESULTS

The measurements of the same patient sample on three different analytical platforms suggested ACTH concentrations below 5 pg/ml. Serial dilutions of serum samples revealed nonlinearity, PEG recovery resulted in ACTH concentrations dropping to < 5 pg/ml, and interferences in plasma were blocked by a heterophilic blocking reagent (21.2 vs < 5 pg/ml), suggesting that assay interference performed on Siemens Immulite led to false-positive ACTH. Finally, the boy was diagnosed with a rare type of ACTH-independent Cushing syndrome.

CONCLUSIONS

The inaccurate evaluation of ACTH misled the physicians, increasing treatment time and diagnostic testing. Thus, an anti-interference workflow should be established between physicians and laboratories to avoid such cases in the future.

ADRENOCORTICOTROPIC HORMONE IMMUNOASSAY INTERFERENCE IN A PATIENT WITH SUBCLINICAL HYPERCORTISOLISM

Context

Immunoassays are vulnerable to occasional analytical errors despite their sensitivity and specificity. Adrenocorticotropic hormone (ACTH) is among hormones which are vulnerable to assay interference.

Objective

In this case report, we aimed to present a case of ACTH interference in a patient with subclinical hypercortisolism.

Case report

We present a case of subclinical hypercortisolism with unexpectedly elevated levels of ACTH in whom interference was shown by different biochemical methods.It is important for the clinician to keep in mind the possibility of interference when clinical and laboratory results are discordant. The communication between the clinician and laboratory staff is important while interpreting results. This case report shows that ACTH interference should be considered in patients with subclinical hypercortisolism who have unexpectedly high levels of adrenocorticotropic hormone.

Diagnostic testing of autonomous cortisol secretion in adrenal incidentalomas

OBJECTIVE

Autonomous cortisol secretion (ACS) is a condition with ACTH-independent cortisol overproduction from adrenal incidentalomas (AI) or adrenal hyperplasia. The hypercortisolism is often mild, and most patients lack typical clinical features of overt Cushing's syndrome (CS). ACS is not well defined and diagnostic tests lack validation.

METHODS

Retrospective study of 165 patients with AI evaluated clinically and by assay of morning plasma ACTH, late-night saliva cortisol, serum DHEA sulphate (DHEAS), 24-h urine-free cortisol, and cortisol after dexamethasone suppression.

RESULTS

Patients with AI (n = 165) were diagnosed as non-functioning incidentalomas (NFI) (n = 82) or ACS (n = 83) according to current European guidelines. Late-night saliva cortisol discriminated poorly between NFI and ACS, showing a high rate of false-positive (23/63) and false-negative (38/69) results. The conventional low-dose dexamethasone suppression test (LDDST) did not improve the diagnostic specificity, compared with the 1 mg overnight DST. Receiver operating characteristic curve analysis of DHEAS in the two cohorts demonstrated an area under the curve of 0.76 (P < 0.01) with a sensitivity for ACS of 58% and a specificity of 80% using the recommended cutoff at 1.04 µmol/L (40 µg/dL).

CONCLUSION

We here demonstrate in a large retrospective cohort of incidentaloma patients, that neither DHEAS, late-night saliva cortisol nor 24-h urine free cortisol are useful to discriminate between non-functioning adrenal incidentalomas and ACS. The conventional LDDST do not add further information compared with the 1 mg overnight DST. Alternative biomarkers are needed to improve the diagnostic workup of ACS.

Management of adrenal incidentalomas: Working through uncertainty

The European society of endocrinology, in association with the European network for the study of adrenal tumors, published recommendations for the diagnosis and treatment of adrenal incidentalomas in 2016. A thorough and critical analysis of the literature was performed to establish evidence-based recommendations and expert suggestions with the aim of avoiding 'over-diagnosis' and 'over-treatment' and to reduce unnecessary investigations, surgery and follow-up. The purpose of this review is to reconsider several recommendations that are open to debate, such as imaging of adrenal incidentalomas, diagnosis of pheochromocytoma, diagnosis and treatment of autonomous cortisol-secreting tumors, investigations of bilateral AI and follow-up of non-operated AIs, based on studies published after the release of the recommendations.

Adrenal insufficiency: Physiology, clinical presentation and diagnostic challenges

Adrenal insufficiency (AI) is a serious condition, which can arise from pathology affecting the adrenal gland itself (primary adrenal insufficiency, PAI), hypothalamic or pituitary pathology (secondary adrenal insufficiency, SAI), or as a result of suppression of the hypothalamic-pituitaryadrenal (HPA) axis by exogenous glucocorticoid therapy (tertiary adrenal insufficiency, TAI). AI is associated with an increase in morbidity and mortality and a reduction in quality of life. In addition, the most common cause of PAI, autoimmune adrenalitis, may be associated with a variety of other autoimmune disorders. Untreated AI can present with chronic fatigue, weight loss and vulnerability to infection. The inability to cope with acute illness or infection can precipitate life-threatening adrenal crisis. It is therefore a critical diagnosis to make in a timely fashion, in order to institute appropriate management, aimed at reversing chronic ill health, preventing acute crises, and restoring quality of life. In this review, we will describe the normal physiology of the HPA axis and explain how knowledge of the physiology of this axis helps us understand the clinical presentation of AI, and forms the basis for the biochemical investigations which lead to the diagnosis of AI.

An Intact ACTH LC-MS/MS Assay as an Arbiter of Clinically Discordant Immunoassay Results

BACKGROUND

Measurement of plasma adrenocorticotropic hormone (ACTH) is key in the differential diagnosis of hypothalamic-pituitary-adrenal disorders. Two-site sandwich immunoassays dominate clinical testing of ACTH in North America; however, discordant results between manufacturers have been repeatedly reported. To resolve the discrepancy, we developed a liquid chromatography–tandem mass spectrometry (LC-MS/MS) assay for the intended measurand, biologically active intact ACTH (iACTH).

METHODS

The multiple reaction monitoring LC-MS/MS assay was designed to selectively measure full-length iACTH, as well as ACTH analogs and fragments (i.e., ACTH1–24 and ACTH18–39). Epitope assignment of the Roche Elecsys antibodies was performed by MALDI-TOF mass spectrometry. A method comparison between Roche Elecsys and Siemens Immulite ACTH immunoassays was performed and clinically concordant/discordant results identified. In a subset of these samples, the iACTH concentration was determined using the LC-MS/MS method.

RESULTS

The lower limit of the measuring interval of the iACTH LC-MS/MS assay was 9 pg/mL (2 pmol/L). The assay was linear from 9 to 1938 pg/mL (2 to 427 pmol/L). Epitope mapping revealed that the Roche capture and detection antibodies bound residues 9–12 and 36–39 of ACTH, respectively. The iACTH LC-MS/MS analysis demonstrated that for discordant results between 2 immunoassays studied, only the Roche results were highly positively correlated with the iACTH concentration.

CONCLUSIONS

Immunoprecipitation of biologically active ACTH molecules followed by LC-MS/MS analysis enabled selective detection of iACTH and relevant biologically active fragments in plasma. Applied to the investigation of clinically discrepant results, this method can act as an arbiter of the concentration of iACTH present.

Falsely elevated plasma ACTH levels measured by the Elecsys assay related to heterophilic antibody in a case of secondary adrenocortical insufficiency

A 49-year-old woman with membranous nephropathy was referred to our hospital during the tapering of oral prednisolone, because of suspicion of primary adrenal insufficiency based on a plasma ACTH level of 399.1 pg/mL in the Elecsys assay and a serum cortisol level of 3.1 μg/dL. A rapid ACTH stimulation test revealed a suboptimal response, whereas a prolonged ACTH simulation test showed a sufficient increase in her urinary free cortisol. Also, big ACTH was not detected by gel exclusion chromatography. Therefore, we speculated that ACTH levels were falsely elevated due to some interference substances. Pretreatment of her plasma with either polyethylene glycol precipitation or a heterophilic blocking tube substantially reduced her ACTH values. When either the Immulite ACTH II or the TOSOH II ACTH was tried instead of the Elecsys ACTH, her plasma ACTH values turned out to be lower and appropriate for her clinical status. These results indicated that heterophilic antibodies interfered only with the Elecsys ACTH assay presumably by bridging the capture and tracer antibodies. To our knowledge, this is the first case in which the Elecsys ACTH assay yielded falsely elevated results. Regardless of the measurement system used, if there is a discordance between assay results and clinical findings, it should be considered to adopt additional procedures and/or another assay.

Heterophile Antibody to Adrenocorticotropin Hormone Interfering with the Investigation of Cushing's Syndrome

The practice of medicine depends on the accuracy of biochemical assays. The high prevalence of incidental masses on imaging necessitates a correct biochemical diagnosis before proceeding to radiological studies. Hormonal assays, tumour markers, and markers of cardiac injury are particularly susceptible to heterophile antibody interference which may lead to inaccurate and misleading results, inappropriate investigation and/or treatment, patient concern and potential harm. A case of heterophile antibody interference in the measurement of ACTH in a patient with Cushing's syndrome resulting in unnecessary invasive investigation is presented. Close collaboration and communication between laboratory and clinical staff is essential where laboratory results and the clinical picture are not congruent.

Autonomous hypercortisolism: definition and clinical implications

In current practice, an adrenal adenoma usually comes as an unexpected byproduct of an imaging study performed for unrelated reasons, without any prior suspect of adrenal disease. Therefore, these tumors currently represent a public health challenge because they are increasingly recognized due to the widespread use of high-resolution cross-sectional imaging for diagnostic purposes. In radiology series, the prevalence of adrenal adenomas increases steeply with age, from around 3% below the age of 50 years up to 10% in the ageing population. These tumors may have clinical relevance because they are able to secrete cortisol autonomously, independently from the pituitary control, in up to 20-30% of patients. In most of the cases the resulting cortisol excess is insufficient to produce a typical Cushing phenotype but may have clinical consequences, such as hypertension, diabetes, obesity, dyslipidemia and osteoporosis. Despite some controversy on the most effective diagnostic algorithm to define this subtle hypercortisolism, there is mounting evidence that a simple approach by using the 1-mg overnight dexamethasone suppression test (DST) may stratify patients for their cardiovascular risk. Cross-sectional, retrospective studies showed that patients with increasingly higher cortisol following DST have an adverse cardiovascular risk profile and are at increased risk of death. Therefore, also a subtle autonomous cortisol excess is associated with increased morbidity and mortality, mainly of cardiovascular origin.

Recent Advances on Subclinical Hypercortisolism

During the last 20 years, a significant body of literature has accumulated regarding subclinical hypercortisolism in patients with adrenal incidentalomas. Retrospective studies have indicated these patients have an increase in cardiovascular events and mortality. Current recommendations for patients with adrenal incidentalomas include an overnight low-dose dexamethasone suppression test and a thorough evaluation of cardiovascular and metabolic risk factors. Further hormonal testing and close monitoring are necessary in patients with incomplete suppression. Unilateral adrenalectomy may be beneficial in cases with abnormal suppression and comorbidities related to hypercortisolemia. Prospective studies are need for a better risk stratification and tailored therapy.