Co-Occurrence of Endogenous and Exogenous Cushing’s Syndromes: Does “Double Cushing Syndrome” Really Exist? A Case Report

Posted on December 1, 2025 by MaryO

ABSTRACT

Double Cushing syndrome exists: exogenous steroid use can mask concurrent adrenal hypercortisolism. When symptoms persist and cortisol remains high after tapering or stopping prescribed glucocorticoids, an endogenous source is likely. Early recognition with ACTH testing, dexamethasone suppression, and adrenal imaging reduces misdiagnosis, favors timely surgery, and supports safe tapering.

1 Introduction

Cushing syndrome (CS) is a non-physiological increase in plasma glucocorticoids [1]. In most cases, the source of increased plasma glucocorticoids is caused by exogenous steroid administration, which is quite common, and about 1% of the world population is on long-term (more than 3 months) oral glucocorticoids [1, 2]. On the contrary, endogenous overproduction of glucocorticoids is rare, and annually, only two to eight per million people are diagnosed with endogenous CS [3]. The simultaneous occurrence of endogenous and exogenous CS is an exceptionally uncommon phenomenon. This dual manifestation has been reported in a few case reports, highlighting its rarity and the complex diagnostic and therapeutic challenges it poses [4, 5]. Therefore, in this study, we discuss a patient who presented with cushingoid features and was simultaneously diagnosed with both endogenous and exogenous CS or, as it is called, double CS.

2 Case Presentation

The patient was a 46-year-old male with a history of new-onset hypertension and recurrent deep vein thrombosis (DVT) who was referred to our endocrinology clinic with a chief complaint of hip pain and weakness of the lower limbs. In the past 3 years, the patient had been receiving 50 mg/day of oral prednisolone and inhalation powder of Umeclidinium and Vilanterol (62.5/25 μg/dose) because of respiratory complications that started after Coronavirus Disease 2019 (COVID-19) vaccination. After 3 months of corticosteroid treatment, he experienced DVT for the first time when he was started on rivaroxaban. However, while he was on treatment, the second DVT occurred 1 month before his referral, and therefore, rivaroxaban was changed to warfarin 5 mg/day.

The patient also mentioned weight gain with his body mass index (BMI) rising from 26 to 31 kg/m2, progressive weakness of proximal muscles, easy bruising, decreased libido, mood changes with mostly euphoric mood, and irritability during the last 2 years. Moreover, multiple osteoporotic fractures of ribs, clavicle, sternum, and lumbar vertebrae were added to his symptoms in the past 5 months. At that time, he underwent bone densitometry, which revealed osteopenia of the left hip with a Z-score of −1.3 and severe osteoporosis of total lumbar spine with a T-score of −3.9. He started taking calcium and vitamin D3 supplements and received a single injection of 750 μg/3 mL teriparatide 30 days before his referral to our center.

Two months ago, the patient gradually reduced the dosage of prednisolone by tapering the dose to 12.5 mg/day. However, a month later, the hip pain and muscle weakness worsened to such an extent that the patient was unable to walk. Due to his signs and symptoms, the patient was referred to our center for further evaluation of CS. The patient also mentioned a history of nephrolithiasis, new-onset hypertension, and lower limb edema, for which he was started on eplerenone 25 mg and furosemide 20 mg tablets once daily. In his family history, the patient’s mother had type 2 diabetes mellitus, and his two sisters had a history of nephrolithiasis. The patient did not mention any history of allergies to medications or foods. He was addicted to opium and had 15 pack-years of smoking, but he did not mention alcohol consumption.

Upon admission, the patient presented with a blood pressure of 150/83 mmHg, heart rate of 74 bpm, respiratory rate of 20/min, temperature of 36.5°C, oxygen saturation of 93%, and BMI of 31 kg/m2. He was sitting in a wheelchair due to weakness and severe pain in the hip. On physical examination, the patient showed the features of CS, including moon face, buffalo hump, central obesity, facial plethora, thin and brittle skin, acne, and purple stretch marks (striae) on the flanks (Figure 1). Proximal muscle weakness in the lower limbs with a muscle force grade of 4/5 and 3+ edema was also observed. Laboratory investigations are shown in Table 1.

Details are in the caption following the image

De-identified clinical photographs illustrating the Cushingoid phenotype. (A) Overall habitus with marked central (truncal) adiposity. (B) Rounded plethoric face (“moon facies”). (C) Relatively slender distal extremities compared with truncal obesity. (D) Dorsocervical fat pad (“buffalo hump”). (E) Upper thoracic/supraclavicular fat accumulation. (F) Protuberant abdomen with wide violaceous striae.
TABLE 1. Laboratory findings of case report.
Laboratory test Patient value (in-hospital) Patient value (follow-up) Reference range
On admission
Hemoglobin (g/dL) 16.6 13.6 13.5–17.5
Hematocrit (%) 49.5 42.1 42–52
WBC (white blood cells; 103/μL) 11.8 7.1 4.0–11.0
PLT (platelet count; 103/μL) 286 294 150–450
BUN (blood urea nitrogen; mg/dL) 10 11 7–18
Cr (creatinine; mg/dL) 0.9 0.9 0.7–1.3
ALP (alkaline phosphatase; IU/L) 1016 129 44–147
AST (aspartate aminotransferase; IU/L) 48 30 < 31
ALT (alanine transaminase; IU/L) 88 21 < 31
CRP (C-reactive protein; mg/dL) 31 3 < 5
ESR (erythrocyte sedimentation rate; mm/h) 63 24 < 15
Sodium (mEq/L) 148 141 136–145
Potassium (mEq/L) 4.8 4.3 3.5–5
FBS (fasting blood glucose; mg/dL) 97 89 80–100
TC (total cholesterol; mg/dL) 267 182 < 200
TG (triglyceride; mg/dL) 148 104 < 200
LDL (low-density lipoprotein; mg/dL) 138 98 < 130
HDL (high-density lipoprotein; mg/dL) 64 55 30–70
In hospital
Cortisol 8 a.m. fasting (μg/dL) 20.2 14.1 4.3–24.9
ACTH (adrenocorticotropic hormone; pg/mL) < 1 — 7.2–63.3
1 mg Overnight dexamethasone suppression test (μg/dL) 16.5 — < 1.8

3 Methods (Differential Diagnosis, Investigations, and Treatment)

Initially suspected of having exogenous-induced CS, the patient’s prednisolone was on hold for 3 days. Cortisol 8 a.m. fasting level, measured with Electrochemiluminescence (ECL) and adrenocorticotropic hormone (ACTH) test, was 20.2 μg/dL (585.4 nmol/L) and < 1 pg/mL, respectively. Due to the lack of suppression of serum cortisol despite not using oral glucocorticoids, the absence of adrenal insufficiency symptoms, and the fact that the patient’s symptoms remained unchanged during this period, co-occurrence of endogenous CS was suspected.

A 1 mg overnight dexamethasone suppression test was performed to confirm endogenous CS diagnosis, and the results were reported as 16.5 μg/dL (normal range < 1.8 μg/dL). Considering the possibility of an ACTH-independent CS, the patient underwent an abdominopelvic multidetector computed tomography (MDCT) of abdominopelvic with adrenal protocol, which revealed a well-defined lesion with an approximate size of 32.8 × 38.6 mm in the left adrenal gland with a radiodensity of 90 Hounsfield units and a normal right adrenal gland (Figure 2). Moreover, evidence of previous old fractures as multiple callus formation was seen involving the clavicles, sternum, bilateral ribs, ischium, and pelvic bones. Multilevel old stable compression fractures of thoracic and lumbar vertebral bodies were also present. The differential diagnoses were glucocorticoid secretory adrenal tumors, including adrenal cell carcinoma and lipid-poor adenoma. In order to rule out pheochromocytoma, 24-h urine catecholamines were measured, and the results were negative.

Details are in the caption following the image

Abdominopelvic multidetector computed tomography (MDCT) with adrenal protocol showing a well-defined lesion with an approximate size of 32.8 × 38.6 mm in the left adrenal gland; radiodensity 90 HU. (A) Transverse plane. (B) Coronal plane. (C) Sagittal plane.

Finally, the patient underwent left adrenalectomy and corticosteroid replacement therapy due to the suppression of the other adrenal gland. According to the post-operative pathological investigations, immunohistochemistry markers reported as negative chromogranin, positive melan-A and inhibin, less than 3% Ki-67 marker, and lipid-poor adrenal cortical adenoma without invasions were diagnosed (Figure 3).

Details are in the caption following the image

Immunohistochemistry of the adrenal lesion (all panels acquired with a 100× oil-immersion objective; 10× eyepiece; original magnification ×1000). (A) Positive inhibin, (B) Positive Melan-A, (C) Less than 3% Ki-67 marker, and (D) Negative chromogranin.

4 Results (Outcome and Follow-Up)

Within 3 months after the operation, the patient’s corticosteroid was tapered and then discontinued due to the normalization of the cortisone serum test (14.1 μg/dL). Proximal limb weakness and hip pain, which had deprived the patient of the ability to move, gradually improved so that he could walk easily and perform daily activities. The signs and symptoms related to CS, including the patient’s mood, skin signs, and general appearance, returned to normal. The patient has been followed up for 6 months after the surgery. The patient’s BMI decreased to 24 kg/m2, and he stopped his anti-hypertensive medications with a blood pressure of 100/60 mmHg without previously prescribed drugs. So far, the laboratory tests have been within the normal range, and he has no complaints (Table 1).

5 Discussion

The described case was diagnosed with a cortisol-producing adrenocortical adenoma accompanied by exogenous CS. CS is an uncommon clinical condition caused by prolonged exposure to increased cortisol levels, which can be due to endogenous or exogenous factors [6]. Endogenous CS is infrequent and is classified as ACTH-dependent (80% of cases) or ACTH-independent (20% of cases) [7]. In the ACTH-independent category, adrenal adenoma accounts for 60% of cases and only 12% of cases of endogenous CS [7, 8]. Exogenous CS mainly occurs due to prolonged administration of glucocorticoids, which are used to manage a broad spectrum of diseases such as inflammatory, autoimmune, or neoplastic disorders and are the most common cause of CS worldwide [9]. Multiple factors, including formulation, duration of administration, pharmacokinetics, affinity, and potency of exogenous glucocorticoids, affect the probability of exogenous CS, but all forms of glucocorticoids can induce CS [10].

In the setting of cushingoid clinical features with chronic administration of high-dose glucocorticoids, especially oral prednisolone, the probability of exogenous CS is remarkably high; therefore, CS diagnostic approaches suggest that the first step after confirmation of cortisol excess is ruling out exogenous glucocorticoid administration [7, 8, 10]. Therefore, the possibility of co-occurrence of endogenous CS with iatrogenic CS is extremely low, and the diagnosis requires high clinical suspicion [4].

Differentiating endogenous and exogenous CS based on clinical features can be challenging and far-fetched. However, a few points can help physicians distinguish between these two. First, exogenous CS symptoms tend to be more striking, while endogenous CS appears more gradually. Second, hypertension, hypokalemia, and features of androgen excess, such as acne and hirsutism, are more common in endogenous CS [4, 10]. In addition, endogenous CS should be suspected if the patient’s symptoms continue after corticosteroid discontinuation or if the serum cortisol level is high despite corticosteroid cessation. In our case, the patient had a high cortisol level despite stopping prednisolone for 3 days, and he did not have any symptoms of adrenal insufficiency despite stopping prednisolone suddenly. Consequently, it was suspected that glucocorticoids might come from an endogenous source. Because ACTH was suppressed concurrently with elevated cortisol, non-ACTH-dependent CS was suspected, and MDCT of abdominopelvic confirmed it.

So far, few similar cases of simultaneous endogenous and exogenous CS have been reported. The first case was a 23-year-old woman with juvenile idiopathic arthritis who was administered high doses of triamcinolone for 16 years [4]. The development of cushingoid features that favored endogenous CS, such as hirsutism and acne, strengthened the suspicion of endogenous CS, and a CT scan revealed hypercortisolism with a bulky and nodular left adrenal gland, and a double CS was confirmed [4]. The second case was a 66-year-old woman diagnosed with exogenous CS after consumption of Traditional Chinese medicine (TCM) for a year [5]. The cessation of TCM did not significantly improve her cushingoid features, and she developed additional CS complications, including hypertension, diabetes mellitus, and osteoporotic fractures over the next 8 years. CS workup revealed a right-sided adrenal adenoma, and after the adrenalectomy, her clinical cushingoid features markedly improved [5]. These cases suggest that exogenous and endogenous CS can exist simultaneously in the same person. Although it is very rare, it should be considered in a person who still complains of CS symptoms after corticosteroid cessation. We suggest clinicians evaluate the patients for the disappearance of exogenous CS symptoms after tapering and stopping glucocorticoids. If the symptoms remain, they should be evaluated for endogenous CS.

6 Conclusion

The co-occurrence of an endogenous CS in the setting of an exogenous CS is curious. The diagnosis is based on a high clinical suspicion. Clinicians should evaluate patients for symptom resolution after tapering and discontinuing corticosteroids. Clinical cushingoid features that do not resolve after discontinuing exogenous glucocorticoids and high cortisol levels despite discontinuing corticosteroids should raise clinicians’ suspicion of the co-occurrence of exogenous and endogenous CS.

Author Contributions

Reza Amani-Beni: investigation, methodology, writing – original draft, writing – review and editing. Atiyeh Karimi Shervedani: methodology, writing – original draft. Bahar Darouei: conceptualization, validation, writing – review and editing. Matin Noroozi: methodology, writing – original draft. Maryam Heidarpour: conceptualization, supervision, validation, writing – review and editing.

Acknowledgments

The authors have nothing to report.

Consent

Written informed consent was obtained from the patient to publish this report, including de-identified clinical photographs, in accordance with the journal’s patient consent policy.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

The data that supports the findings of this study are available on request of the corresponding author. The data are not publicly available due to privacy restrictions.

https://onlinelibrary.wiley.com/doi/10.1002/ccr3.71419

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Metyrapone Benefits Blood Pressure in Mild Hypercortisolism

Posted on November 7, 2025 by MaryO

TOPLINE:

A notable proportion of patients with mild hypercortisolism achieved blood pressure (BP) control with low-dose evening metyrapone, without requiring the intensification of antihypertensive therapy. The treatment was particularly beneficial for those with higher baseline systolic BP and was well tolerated, with no adverse events reported.

METHODOLOGY:

  • This prospective observational study assessed the impact of low-dose evening metyrapone on 24-hour ambulatory BP, glucose metabolism, and the cortisol circadian rhythm in 20 patients with mild hypercortisolism (median age, 70.5 years; 65% women).
  • Eligible patients had cortisol levels > 1.8 μg/dL after a 1-mg dexamethasone suppression test on at least two separate occasions, fewer than two specific Cushing syndrome‑related symptoms, and either hypertension or impaired glucose metabolism.
  • Patients received evening metyrapone 250 mg/d, with dose adjustments on the basis of clinical response and cortisol secretion; in 12 patients who showed no signs of hypoadrenalism after week 12, an additional 250-mg afternoon dose was given.
  • The primary endpoint was BP control, defined as a reduction in mean 24-hour systolic BP of ≥ 5 mm Hg without increasing antihypertensive medication; ambulatory BP monitoring was done at baseline and weeks 12 and 24.

TAKEAWAY:

  • At 24 weeks, 40% of patients had a clinically significant improvement in BP control without escalation of therapy, with reductions in both daytime and nighttime systolic BP; benefits were more pronounced in those with elevated baseline systolic BP.
  • Glucometabolic control improved in four patients at 24 weeks; those with poorly controlled type 2 diabetes at baseline achieved the most pronounced glycaemic benefits.
  • Salivary cortisol levels remained unchanged from baseline; no significant changes in hormonal, metabolic, or anthropometric parameters were observed from baseline, except for testosterone levels in women.
  • The treatment was well tolerated, with no side effects or reports of adrenal insufficiency.

IN PRACTICE:

“Our findings support the notion that metyrapone may offer clinical benefits in patients with mH [mild hypercortisolism], particularly those with uncontrolled comorbidities. The observed improvements in BP and glycaemic control, despite minimal changes in UFC [urinary free cortisol] levels, underscore the need to re-evaluate traditional therapeutic targets and to adopt a more holistic approach to disease management,” the authors of the study wrote.

SOURCE:

This study was led by Antonio Musolino, University of Milan, Milan, Italy. It was published online on October 16, 2025, in the European Journal of Endocrinology.

LIMITATIONS:

This study was limited by its relatively short treatment duration, potential adherence bias, and an older cohort age, which may have limited generalisability. The sample size, although adequate for the primary endpoint, was limited. The absence of a control group restricted the ability to definitively attribute improvements to metyrapone therapy.

DISCLOSURES:

This study received financial support through an investigator-initiated study grant from ESTEVE (formerly HRA RD). Two authors reported receiving speaker or consultancy fees or honoraria from Corcept Therapeutics.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication

https://www.medscape.com/viewarticle/metyrapone-benefits-blood-pressure-mild-hypercortisolism-2025a1000szc?form=fpf

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Cushing Syndrome Test Choice Should Fit Patient Factors & Disease Stage

Posted on October 20, 2025 by MaryO

Caused by excessive exposure to the hormone cortisol, endogenous Cushing syndrome (CS) is difficult to diagnose. Currently available biochemical tests that assess cortisol production have limited diagnostic specificity and sensitivity, and their performance can vary depending on the patient, according to a review article in Current Opinion in Endocrinology, Diabetes and Obesity.

“Whether performed on blood, urine, saliva, or hair, all biochemical tests for CS have advantages and disadvantages. It is therefore essential to select them based on the individual characteristics of the patient and the stage of the disease in order to improve their diagnostic performance,” wrote corresponding author Antoine Tabarin, MD, and coauthor Amandine Ferriere, MD, of the University Hospital of Bordeaux in Pessac, France.

The Endocrine Society recommends initial screening of patients with suspected CS using 24-hour urinary-free cortisol (UFC), late-night salivary cortisol (LNSC), or the overnight dexamethasone suppression test (ONDST). To avoid false negatives from variability in cortisol production, UFC and LNSC tests should be performed twice.

Among the three screening options, meta-analysis findings suggest comparable diagnostic performance, the authors reported.

“However, they also concluded that these investigations should not be used indiscriminately,” the review continued, “and should be selected according to various circumstances.”

ONDST results can be affected by medications, age, a history of bariatric surgery, and even individual differences in dexamethasone metabolism, according to the review. UFC requires patient education and a complete 24-hour urine collection. LNSC testing, which biochemically assesses the loss of circadian rhythmicity consistent in CS, may not be appropriate for people with highly variable sleep schedules, including shift workers.

For early detection of Cushing disease (CD) recurrence after pituitary surgery, LNSC is the recommended first-line procedure for biochemical follow-up. LNSC is also the tool of choice for monitoring patients with CS treated with medication, the article reported.

For patients with adrenocorticotropic hormone (ACTH)-dependent CS, UFC offers high accuracy for assessing the likelihood of CD and ectopic adrenocorticotropin. However, for the diagnosis of cyclical or intermittent CS, repeat UFC tests are “cumbersome and nearly impossible,” the authors wrote.

LNSC, on the other hand, allows for frequent daily assessment of cortisol secretion which is helpful for identifying cyclical CS. Similarly, measurements of cortisol and cortisone levels in the hair can assess mid- to long-term tissular exposure to cortisol and signal cyclical CS as well, the review explained.

References

Ferriere A, et al. Curr Opin Endocrinol Diabetes Obes. 2025;32(5):233-239. doi:10.1097/MED.0000000000000923

From https://www.physiciansweekly.com/post/cushing-syndrome-test-choice-should-fit-patient-factors-disease-stage

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The Impact of Adrenalectomy On Metabolic Outcomes of Patients Wwth Mild Autonomous Cortisol Secretion Defined by Low-Dose Dexamethasone Suppression Testing

Posted on October 12, 2025 by MaryO

Abstract

Background

Up to 50% of patients with adrenal incidentalomas have mild autonomous cortisol secretion, which may increase their cardiometabolic morbidity, compared with patients with nonfunctional adrenal tumors. Studies evaluating cardiometabolic outcomes of patients with mild autonomous cortisol secretion defined by 1-mg dexamethasone suppression testing (cortisol 1.8–5 μg/dL) have demonstrated mixed results. The aim of this study was to assess the metabolic outcomes of patients with mild autonomous cortisol secretion, defined by the 1-mg dexamethasone suppression testing criterion, compared with patients with nonfunctional adrenal tumors who underwent adrenalectomy.

Methods

We conducted a single-institution retrospective cohort study comparing adult patients who underwent unilateral adrenalectomy from November 30, 2011, to August 19, 2023, for mild autonomous cortisol secretion (1-mg dexamethasone suppression testing cortisol 1.8–5 μg/dL) or nonfunctional adrenal tumors (1-mg dexamethasone suppression testing cortisol <1.8 μg/dL). Preoperative prevalences and postoperative changes in diabetes mellitus, hypertension, dyslipidemia, and elevated body mass index (≥25) were assessed. Patients were followed from the time of surgery until their last outpatient visit. Multivariable logistic regression was pursued for outcomes that varied between cohorts.

Results

A total of 65 patients (53 mild autonomous cortisol secretion and 12 nonfunctional adrenal tumors) were analyzed. Patients with mild autonomous cortisol secretion were older and more likely to have diabetes mellitus than patients with nonfunctional adrenal tumors (odds ratio: 7.81, 95% confidence interval [0.94, 64.96], P = .04). Patients were followed for a median of 28.1 months [11.1, 55.3 months]. Patients with mild autonomous cortisol secretion were more likely to have postoperative weight improvement (odds ratio: 8.31, [0.97, 71.14], P = .03). After adjusting for clinically relevant variables, the 1-mg dexamethasone suppression testing cortisol was predictive of postoperative weight improvement (odds ratio: 1.88, [1.1, 3.65], P = .04).

Conclusion

Weight loss should be considered as a potential benefit of adrenalectomy in patients with mild autonomous cortisol secretion.

Introduction

Mild autonomous cortisol secretion (MACS) is the most common hormonal abnormality diagnosed in patients with adrenal incidentalomas, impacting 20%–50% of patients.1 Patients with MACS have biochemical evidence of adrenocorticotropic hormone (ACTH)-independent hypercortisolism but lack clinical stigmata commonly associated with overt hypercortisolism, such as facial plethora, abdominal adiposity, extremity weakness and wasting, and/or violaceous striae.2 Overt hypercortisolism is well recognized to cause cardiovascular, musculoskeletal, and metabolic disorders, which have variable resolution even after diagnosis and treatment.3 There is a growing body of evidence that patients with MACS also have increased cardiometabolic morbidity and mortality compared with patients with nonfunctional adrenal tumors,4 but this evidence is challenging to interpret given wide variability in diagnostic criteria that have historically been used.5, 6, 7
Recent guidelines have suggested that a diagnosis of MACS be applied to all patients with a morning (AM) serum cortisol of >1.8 μg/dL after low-dose (1-mg) dexamethasone suppression testing (DST) who lack overt features of hypercortisolism.8,9 However, prior studies comparing cardiometabolic outcomes between patients with MACS and nonfunctional adrenal tumors as well as between patients who underwent operative and nonoperative management have used a 1-mg DST AM serum cortisol of 1.8–5.0 μg/dL as a definition of mild (“subclinical”) hypercortisolism.10, 11, 12, 13, 14, 15, 16 Given that these studies have demonstrated mixed results,4 the primary aim of this study was to assess the metabolic outcomes of patients with MACS, as defined by a 1-mg DST AM cortisol of 1.8–5.0 μg/dL, compared with patients with nonfunctional adrenal tumors who underwent adrenalectomy.

Section snippets

Methods

This was a single-institution retrospective cohort study of patients aged ≥18 years who underwent initial unilateral adrenalectomy from November 30, 2011, to August 19, 2023. Patients were identified through a prospectively maintained database of all patients who underwent adrenalectomy at the study institution. Patients were excluded if they had a 1-mg DST AM serum cortisol of >5 μg/dL, ACTH-dependent hypercortisolism, primary aldosteronism, pheochromocytoma, primary bilateral macronodular

Results

Of the 460 patients who underwent adrenalectomy during the study period, 53 patients met criteria for MACS and 12 patients for nonfunctional adrenal tumors, yielding a cohort of 65 patients. Patients with MACS were older than those with nonfunctional adrenal tumors (MACS, median 60 years [IQR: 54, 68 years] vs nonfunctional adrenal tumors, 49 years [37, 57 years], P = .02) but were similar by sex, race, ethnicity, BMI, nodule size, laterality, and surgical approach (Table II). Among patients

Discussion

MACS is the most common hormonal abnormality diagnosed in patients with adrenal incidentalomas. Despite lacking clinical stigmata of overt hypercortisolism, patients with MACS appear to have increased cardiometabolic morbidity and mortality similar to patients with overt hypercortisolism. The optimal management of MACS is debated, and prior studies using a 1-mg DST AM serum cortisol of 1.8–5.0 μg/dL as a definition of mild hypercortisolism have demonstrated mixed results. Hence, this study

Funding/Support

This project is funded in part by the Advancing a Healthier Wisconsin Endowment at the Medical College of Wisconsin. This publication was supported by the National Center for Research Resources and the National Center for Advancing Translational Sciences, National Institutes of Health (NIH), through grant number UL1TR001436. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIH. The grant supports the creation and maintenance of

CRediT authorship contribution statement

Alexa Lisevick Kumar: Writing – original draft, Visualization, Methodology, Formal analysis, Data curation, Conceptualization. Sophie Dream: Writing – review & editing, Validation, Supervision, Methodology, Investigation. Tahseen Shaik: Resources, Project administration, Investigation, Data curation. Kara Doffek: Resources, Project administration, Investigation, Data curation. Ryan Conrardy: Writing – review & editing, Methodology, Formal analysis. James W. Findling: Writing – review & editing,

Conflict of Interest/Disclosure

Dr Findling reports consulting for Corcept, Diurnal, Crinetics and serving as an investigator for Recordati. The rest of the authors reported no biomedical financial interests or potential conflicts of interest.

References (34)

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    Cushing’s syndrome: update on signs, symptoms and biochemical screening

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  • S. Puglisi et al.

    Long-term consequences of cushing syndrome: a systematic literature review

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  • I.C.M. Pelsma et al.

    Comorbidities in mild autonomous cortisol secretion and the effect of treatment: systematic review and meta-analysis

    Eur J Endocrinol

    (2023)
  • X. Ren et al.

    Evaluating the efficacy of surgical and conservative approaches in mild autonomous cortisol secretion: a meta-analysis

    Front Endocrinol (Lausanne)

    (2024)
  • M.M. Khadembashiri et al.

    Comparison of adrenalectomy with conservative treatment on mild autonomous cortisol secretion: a systematic review and meta-analysis

    Front Endocrinol

    (2024)
  • Y.S. Elhassan et al.

    Natural history of adrenal incidentalomas with and without mild autonomous cortisol excess

    Ann Intern Med

    (2019)
  • M. Fassnacht et al.

    European society of endocrinology clinical practice guidelines on the management of adrenal incidentalomas, in collaboration with the European network for the study of adrenal tumors

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    American association of endocrine surgeons guidelines for adrenalectomy: executive summary

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The Reflex Dexamethasone Suppression Test: Development and Assessment of Reflexed Serum Dexamethasone Measurement for the Diagnosis of Cushing Syndrome

Posted on August 23, 2025 by MaryO

Abstract

Background

Screening for Cushing syndrome (CS; endogenous overproduction of ACTH or cortisol) is performed by the low-dose overnight serum dexamethasone suppression test (oDST) with the measurement of serum dexamethasone concentration to assure an effective dose.

Objective

We evaluated the utility of only measuring serum dexamethasone in samples with nonsuppressed serum cortisol using a conservative serum cortisol cutoff.

Methods

This retrospective study included 261 oDSTs completed before Reflex implementation (Pre-Reflex-oDST) and 281 oDSTs completed after (Post-Reflex-oDST). Serum cortisol and serum dexamethasone data were paired to the diagnosis and analyzed with comparative statistical tests and receiver operating characteristic curve (ROC) analysis.

Results

Endogenous hypercortisolism was diagnosed in 38 of 261 Pre-Reflex-oDSTs (14%) and 40 of 281 (14%) Post-Reflex-oDSTs. In oDSTs with SerCort >1.8 mcg/dL, there were 9% and 6% false positives in the Pre-vs Post-Reflex-oDST group, respectively. In the Pre-Reflex-oDST group, the median SerCort was 1.1 mcg/dL (95% CI: 0.8–1.5) in patients without CS and 3.9 mcg/dL (95% CI: 2.6–7.9) in those with CS (P < 0.001). The optimal ROC cutoff of SerCort in the Pre-Reflex-oDST group was 2.1 mcg/dL (sensitivity 92%, specificity 93%). In the Post-Reflex-oDST group, the median SerCort was 1.1 mcg/dL (95% CI: 0.8–1.5) in patients without CS and 2.9 mcg/dL (95% CI: 2.6–7.9) in those with CS (P < 0.001). The optimal ROC cutoff of SerCort in the Post-Reflex-oDST group was 2.1 mcg/dL (sensitivity 95%, specificity 93%; not different from Pre-Reflex-oDST group).

Conclusion

Reflex measurement of the serum dexamethasone did not affect oDST test performance while reducing costs.

Abbreviations

CS

Cushing syndrome
oDST

low-dose overnight serum dexamethasone suppression test
ROC

receiver operating characteristic
NH

neoplastic hypercortisolism
NNH

non-neoplastic hypercortisolism
HPA

hypothalamic pituitary adrenal
SerCort

serum cortisol
SerDex

serum dexamethasone
WDL

Wisconsin Diagnostic Laboratories
LOQ

limit of quantification
UFC

urine free cortisol

Highlights

  • •
    Reflexing only nonsuppressed serum cortisol samples for the measurement of serum dexamethasone does not negatively affect the performance of the overnight low-dose DST (oDST)
  • •
    Reflex implementation greatly reduced the number of serum dexamethasone measurements thereby decreasing unnecessary costs
  • •
    The oDST appeared to be valid as long as there was a measurable serum dexamethasone result (>50 ng/dL)

Clinical Relevance

We report a novel Reflex overnight dexamethasone suppression test (oDST) serum dexamethasone measurement protocol with the benefit of greatly lowering costs without loss of oDST performance supporting its implementation in screening for Cushing syndrome.

Introduction

Endogenous Cushing syndrome (CS) includes neoplastic hypercortisolism either due to autonomous cortisol production or excessive ACTH secretion.1 Non-neoplastic hypercortisolism (NNH) is also an important clinical entity that is characterized as bona fide cortisol excess caused by conditions such as depression, chronic kidney disease, and poorly controlled diabetes.2, 3, 4 Chronically elevated cortisol levels contribute to significant morbidity and mortality due to cardiovascular, metabolic, musculoskeletal, and immunologic effects, including hypertension, diabetes, osteoporosis, and increased susceptibility to infections5,6 leading to prolonged disease burden and worsening clinical outcomes.2,3
Biochemical evaluation is indicated for individuals presenting with features of hypercortisolism, as well as for those with adrenal incidentalomas, regardless of symptoms, in accordance with current guidelines.7 However, the workup is complicated by varying severities of hypercortisolism and diurnal rhythm of endogenous cortisol requiring screening tests to take advantage of predictable nadirs and negative feedback.1 One of the current first-line screening tests for CS is the 1 mg (low dose) overnight dexamethasone suppression test (oDST).8 Positive oDST results require additional testing such as late-night salivary cortisol and 24 h urine free cortisol measurements.8, 9, 10
The oDST takes advantage of decreased HPA negative feedback sensitivity in CS.11 An oral 1 mg dexamethasone dose is given between 2300 hours and 2400 hours and serum cortisol (SerCort) is then measured at 0800 h the following morning with levels <1.8 mcg/dL (50 nmol/L) representing normal suppression.8 A clinical sensitivity of 95% highlights the oDST as a useful screening tool; however, a specificity of ∼80% indicates a greater potential for false-positive results.10,12 A higher burden of false-positive results complicates diagnosis, leading to further testing, delays in diagnosis and treatment, and increased costs and resource utilization for both patients and the health care system. Therefore, the measurement of a serum dexamethasone (SerDex) in the next morning SerCort sample should identify insufficient SerDex levels that may result from factors such as mistiming of, or altogether missing the dexamethasone dose, differences in dexamethasone metabolism, variation in gastrointestinal absorption, increased cortisol binding globulin (eg, due to oral contraceptives), and medications that alter CYP3A4 activity.13, 14, 15, 16, 17
To reduce unnecessary and costly SerDex measurements, our institution implemented in 2023 a Reflex protocol in which SerDex is only measured if post-oDST SerCort is ≥ 1.6 mcg/dL (ie nonsuppressed). This approach was suggested but not evaluated by Genere et al.18 Since the purpose of this study was not to validate the concept of the oDST, we chose 1.6 mcg/dL as a conservative cutoff so that borderline SerCort with small variations around the accepted 1.8 mcg/dL cutoff would not bias the results. This study assessed equivalency in test performance between Pre- and Post-Reflex-oDST implementation and estimated the associated cost savings. As a secondary outcome, we evaluated therapeutic SerDex levels necessary for valid testing.

Materials and Methods

Study Design

A retrospective cohort study was performed on all oDSTs completed at Froedtert & the Medical College of Wisconsin and the affiliated Wisconsin Diagnostic Laboratories between May 2023 and April 2024. This study was approved by the Medical College of Wisconsin Institutional Review Board as a Quality Improvement Project under PRO00050802. All data in the database were de-identified and coded.

Study Population

The study population included patients aged ≥18 years who completed a oDST in the outpatient setting through the system with serum samples processed through Wisconsin Diagnostic Laboratories. Cohorts were divided into Pre- and Post-Reflex-oDST groups based on the date of Reflex implementation described below (October 31, 2023), with the Pre-Reflex-oDST group consisting of tests performed in the 6 months prior and the Post-Reflex-oDST group including tests from the 6 months following implementation. The ordering clinician still had the option to choose oDST AM cortisol alone without ordering a SerDex measurement. Exclusion criteria included repeat oDST for the same patient within the same 6-month period (Pre- or Post-Reflex-oDST groups); however, results from patients who underwent oDST during both the Pre- and Post-Reflex-oDST periods were included. Patients with SerDex <50 ng/dL were also excluded. At this time, all patients included in the analysis had either a confirmed hypercortisolism diagnosis or were determined not to have pathophysiological hypercortisolism based on clinical and biochemical evaluation.8 A combination of biochemical tests (24-hour free urine cortisol, late-night salivary cortisol, oDST), imaging (adrenal and pituitary CT/MRI), and other testing (DDVAP testing, surgical outcome, biopsy) were used to confirm the diagnosis of CS per the current guidelines.8 Hypercortisolism included both neoplastic causes (CS) and non-neoplastic causes (NNH).2 In our study, NNH included patients with chronic nausea and weight loss, chronic kidney disease, poorly controlled diabetes, excess alcohol intake, obesity with physiological stress, chronic pain, and opioid withdrawal. For simplicity, all hypercortisolism patients are abbreviated “CS” whether neoplastic or non-neoplastic.

Procedures

Patients were instructed to take 1 mg of dexamethasone at 11:00 pm and then had their blood sampled the next morning between 8:00 and 9:00 am SerCort level was measured using the Roche Elecsys Cortisol II Electrochemiluminescence immunoassay performed on a Cobas e801 module.19 In the Pre-Reflex-oDST group, individual orders for serum cortisol and dexamethasone were placed by the provider. Both tests were performed, regardless of the subsequently reported oDST serum cortisol value. In the Post-Reflex-oDST group, a single “Dexamethasone Suppression Cortisol Reflex” order was placed, that prompted a SerCort measurement. If SerCort was ≥1.6 mcg/dL (ie, nonsuppressed), an electronic order for a SerDex send-out measurement was automatically placed by the laboratory information system. The laboratory’s automated processing line removed the serum sample from storage, created an aliquot and placed it in a queue for samples to be sent to ARUP Laboratories. ARUP Laboratories measured SerDex by liquid chromatography-mass spectrometry (limit of quantitation [LOQ] = 50 ng/dL; reference interval: 140 – 295 ng/dL; https://ltd.aruplab.com/Tests/Pub/2003248).

Data Collection

Data acquired from each oDST, including date and time of collection, SerCort, and SerDex, were extracted from the laboratory information system. Additional data, including demographics, CS diagnosis, and treatment were collected from the electronic health record and securely stored in RedCAP (version 15.0.2; Nashville, TN). Patients with inconclusive test results were followed for several months after oDST until a diagnosis was established through additional testing and/or clinical evaluation.

Outcomes Assessment

The primary outcome of this study was to quantify the number of SerDex tests avoided while assessing whether implementation of the Reflex oDST affected overall test performance in the screening for endogenous hypercortisolism. Equivalency between Pre- and Post-Reflex-oDSTs was defined by the similarities in prevalence of a new diagnosis, average SerCort by diagnosis, and SerCort cutoffs by receiver operating characteristic (ROC) curve AUC, and optimal cutoff values. Secondary outcomes included quantification of avoided SerDex measurements to estimate the cost savings associated with Reflex implementation using the US Medicare Reimbursement Rate [20 Accessed 4/1/2025; CPT code 80 299)]. We also evaluated suppressed oDST’s SerDex concentrations to determine if there was a correlation between SerDex level achieved and the degree of suppression of SerCort.

Statistical Analysis

All statistical analyses were performed using Sigmaplot 15.0 (RRID:SCR_003210; https://scicrunch.org/resolver/SCR_003210; Systat Software, Inc, Inpixon, Palo Alto, CA). Continuous variables that were not normally distributed are presented as the median and interquartile ranges. Demographic data were analyzed by two-way analysis of variance and chi-square. Differences in SerCort and SerDex between Pre- and Post-Reflex-oDST groups and CS diagnosis were tested by Mann-Whitney U test and t-test. Optimal cutoff values for each group were determined by ROC analysis using Youden’s index and AUCs were compared with a DeLong test. A P value <0.05 was considered statistically significant. Post-hoc power analyses results are provided where appropriate.

Results

Study Population Characteristics

A total of 616 oDSTs (308 in the Pre-Reflex-oDST and 308 in the Post-Reflex-oDST groups) were screened for eligibility (Fig. 1). After excluding oDSTs with SerDex below the LOQ (n = 12) and repeated oDSTs in the same patient (n = 62), a total of 542 oDSTs were included for analysis. Demographic data are presented in Table 1. The without CS group was younger than the patients with CS group in both Pre- and Post-Reflex-oDST groups. There were no differences in the distribution of race between the groups with and without CS groups and the Pre-vs Post-Reflex-oDST groups. There were more females regardless of diagnosis, but the sex distribution was not different Pre vs Post-Reflex-oDST implementation.

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Figure 1. Flowchart of participants selection from 616 completed oDSTs completed 6 months before (n = 308) and after (n = 308) Reflex implementation. Subsequent oDSTs for the same patient and unmeasurable post-oDST serum dexamethasone (SerDex) (<50 ng/dL [Lower quantifiable limit]) were excluded from analysis. A total of 542 oDSTs were included for analysis and breakdown of CS diagnosis and etiology are shown. ACTH-dependent CS is further broken down to differentiate neoplastic (NH) versus non-neoplastic (NNH) etiologies. CS = Cushing Syndrome; NH = neoplastic hypercortisolism; NNH = nonneoplastic hypercortisolism; oDST = overnight dexamethasone suppression test; SerDex = serum dexamethasone.

Table 1. Demographic Characteristics of Patients Who Underwent oDST Before and After Reflex Implementation

Empty Cell Pre-Reflex Post-Reflex
Yes CS with NNH Yes CS without NNH No CS Yes CS with NNH Yes CS without NNH No CS
N 38 34 223 40 38 241
Age
 Mean (SD) 63.6 (13.8) 63.8 (14.4) 56.0 (15.1)a 63.8 (13.2) 63.1 (13.1) 55.3 (15.5)b
Sex
 Male (%) 6 (15.8) 4 (11.8) 57 (25.6) 11 (27.5) 11 (28.9) 67 (27.8)
 Female (%) 32 (84.2) 30 (88.2) 166 (74.4) 29 (72.5) 27 (71.1) 174 (72.2)
Race
 American Indian or Alaskan Native (%) 0 0 1 (0.4) 0 0 1 (0.4)
 Asian (%) 0 0 3 (1.3) 0 0 1 (0.4)
 Black or African American (%) 5 (13.2) 5 (14.7) 27 (12.2) 6 (15.0) 6 (15.8) 23 (9.5)
 Other (%) 2 (5.3) 1 (2.9) 8 (3.6) 1 (2.5) 1 (2.2) 9 (3.8)
 White (%) 31 (81.5) 28 (82.4) 184 (82.5) 33 (82.5) 31 (82.0) 207 (85.9)
Data are further stratified by Cushing syndrome (CS) diagnosis. Age is presented as mean (SD); sex and race as counts (percentages).
a
Age different from group with CS within Pre-Reflex-oDST (P = 0.005).
b
Age different from group with CS within Post-Reflex-oDST (P < 0.001) regardless of whether NNH cases are included. Male vs female distribution NS (χ2 = 2.533, 3 df, P = 0.469). Race distribution NS (χ2 = 4.37733, 12 df, P = 0.976).
Within the Pre-Reflex-oDST group, 38 patients (14%) were diagnosed with endogenous hypercortisolism (CS) with 13 being ACTH-dependent (9 pituitary and 4 non-neoplastic hypercortisolism) and 25 being ACTH-independent. Within the Post-Reflex-oDST group, 40 patients (14%) were diagnosed with CS with 11 being ACTH-dependent (8 pituitary, 2 non-neoplastic, and 1 ectopic ACTH) and 25 being ACTH-independent.

Prereflex-oDST vs Post-reflex-oDST Analysis

In the Pre-Reflex-oDST group, out of the 261 included subjects, 172 oDSTs (65%) suppressed to <1.6 mcg/dL, meaning that only 89 tests would have undergone reflex SerDex measurements after implementation of Reflex testing. Among these, 51 were determined not to have CS. In the Post-Reflex-oDST group, out of 281 subjects, 191 oDSTs (68%) suppressed to <1.6 mcg/dL, resulting in 90 reflexed SerDex measurements, of which 50 did not have CS. Within the Pre-Reflex-oDST group, there were 38 patients who had CS and in the Post-Reflex-oDST group 40 patients were found to have CS. There was no difference in CS prevalence between the Pre- and Post-Reflex-oDST groups (P = 0.52). Among oDSTs with SerCort levels >1.8 mcg/dL [the conventional cutoff 8], 24/262 (9% false positive) in the Pre-Reflex-oDST group and 21/281 (7% false positive) in the Post-Reflex-oDST group were later determined not to have CS by standard guidelines criteria.8 Reflex implementation resulted in a reduction of the number of SerDex measurements by 68% resulting in cost savings of at least $18.64 per ordered oDST.
In the Pre-Reflex-oDST group, the median SerCort was 1.1 mcg/dL (95% CI: 0.8–1.5) in patients who did not have CS and 3.9 mcg/dL (95% CI: 2.6–7.9) in those who had CS (P < 0.001). In the Post-Reflex-oDST group, the median SerCort was also 1.1 mcg/dL (95% CI: 0.8–1.5) in patients who did not have CS and 2.9 mcg/dL (95% CI: 2.6–7.9) in those who had CS (P < 0.001) (Fig. 2). There was no difference comparing the CS diagnosis status between Pre- and Post-Reflex-oDST groups. There was still no difference in median SerCort in patients with CS when comparing the Pre- and Post-Reflex-oDST groups with NNH cases excluded (P = 0.269). Furthermore, the NNH patients were biochemically indistinguishable from patients with neoplastic hypercortisolism (NH). In fact, when we compared post-oDST cortisol between NH (3.6 [2.4-7.7; N = 72) and NNH (3.4 [2.7-8.5; N = 6]), the P value was 0.729. There was also no difference between CS NH with NNH included vs CS NH excluding NH within the Pre-Reflex-oDST group and within the Post-Reflex-oDST group.

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Figure 2. Comparison of oDST serum cortisol (SerCort) levels Pre-vs Post-Reflex-oDST implementation. The medians are further stratified based on whether the patient did not have Cushing Syndrome (No CS – red) and those who had CS (Yes CS – blue). Each box represents the interquartile range and the horizontal line within represents the median. The error bars represent the 10th-90th percentiles and dots represent results outlying the 10th-90th percentiles. a, denotes significant difference of median SerCort levels between no CS vs CS in both Pre- and Post-Reflex-oDST groups (P < 0.001). There was no difference in medians following exclusion of NNH from Yes CS in both Pre- and Post-Reflex-oDST groups (P = 0.269). CS = Cushing Syndrome; NH = neoplastic hypercortisolism; NNH = nonneoplastic hypercortisolism; oDST = overnight dexamethasone suppression test; SerDex = serum dexamethasone.

A power analysis was performed to compare Pre-reflex oDST to Post-Reflex oDST SerCort values in patients with CS with the null hypothesis that there was no effect of implementing the reflex approach. Assuming a clinically significant effect of implementing the reflex test (a difference of oDST serum cortisol of 2 mcg/dL with a conservative SD of the difference of 2.5 mcg/dL) with sample sizes of 38 Pre-Reflex and 40 Post-Reflex in our study, the power was 0.937 with an alpha of 0.050. With an expected difference in serum cortisol of 0.8 mcg/dL and an SD of the difference of 1.0 mcg/dL, the power was 0.937 with an alpha of 0.05. Considering that the patients before and after reflex implementation were from the same population, institution, and ordering clinicians, we are confident that the Reflex testing did not influence the oDST performance and the laboratory data outcomes.
There was also no difference in SerCort between Pre- and Post-Reflex-oDST tests in the predictive performance for CS. The ROC curve AUC of SerCort in both the Pre- and Post-Reflex periods was 0.97. The optimal ROC cutoff of SerCort in the Pre-Reflex-oDST group was 2.1 mcg/dL (sensitivity 92%, specificity 93%). The optimal ROC cutoff of SerCort in the Post-Reflex-oDST group was 2.1 mcg/dL (sensitivity 95%, specificity 93%; not different from Pre-Reflex-oDST group) (Table 2). When NNH cases were excluded and ROC curves were rerun, there was no difference in ROC curve area, optimal SerCort cutoff values, or sensitivity and specificity in Pre- and Post-Reflex-oDST groups.

Table 2. Receiver operating characteristic (ROC) analysis of oDST SerCort results for Pre-vs Post-Reflex-oDST groups. A. Analysis including NNH patients are at the top; B. Analysis excluding NNH patients are at the bottom

Empty Cell Pre-Reflex Post-Reflex
A. Including NNH patients
 ROC Curve Area (SE) 0.97 (0.01) 0.97 (0.01)
 95% confidence interval 0.96-0.99 0.95-0.99
 P value P < 0.0001 P < 0.0001
 Sample size: No CS/Yes CS 223/38 241/40
Cutoff Sensitivity Specificity Cutoff Sensitivity Specificity
 Optimal 8 AM SerCort Cutoff (mcg/dL) 2.1 92% 93% 2.1 95% 93%
Empty Cell Pre-Reflex without NNH Post-Reflex without NNH
B. Excluding NNH patients
 ROC curve area (SE) 0.97 (0.01) 0.97 (0.01)
 95% confidence interval 0.96-0.99 0.95-0.99
 P Value P < 0.0001 P < 0.0001
 Sample size: No CS/Yes CS 223/34 241/38
Cutoff Sensitivity Specificity Cutoff Sensitivity Specificity
 Optimal 8 AM SerCort Cutoff (mcg/dL) 2.1 91% 92% 2.1 95% 93%
Area under the curve (AUC) was calculated and compared with a DeLong test (AUC = 0.97, P < 0.0001, for both). Using Youden’s Index, optimal cutoff values were determined by maximizing sensitivity and specificity. When ROC rerun without NNH, the sensitivity and specificity did not change in both Pre- and Post-oDST-Reflex groups.

Prereflex-oDST Comparison of SerDex vs SerCort

In comparing the Pre-Reflex-oDST group SerDex results of <140 ng/dL versus >140 ng/dL (the lower reference limit of the SerDex assay), median SerCort was 1.2 mcg/dL and 1.1 mcg/dL, respectively (P = 0.621) (Fig. 3A). The scatter regression plot illustrates that there was no relationship between SerDex (ng/dL) and SerCort (mcg/dL) by CS diagnosis (Fig. 3B). Each point represents an individual oDST, with red indicating patients who did not have CS (n = 223) and blue indicating those who had CS (n = 38). In patients who did not have CS, SerDex ranged from 61.5 to 908.9 ng/dL whereas in patients who had CS, SerDex ranged from 96.3 to 646.0 ng/dL. Theoretical linear regression lines are shown. In fact, no significant correlation between SerDex and SerCort was found in the group who did not have CS (r = 0.002; P = 0.972) nor the group who had CS (r = 0.114; P = 0.494) so the regression lines are only provided for visual clarity. When NNH cases were excluded, there was still no correlation between SerDex and SerCort in patients with CS (P = 0.432). Furthermore, analysis of only NNH cases also showed no correlation between SerDex and SerCort (P = 0.871).

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Figure 3. Comparison of post-oDST serum cortisol (SerCort) to serum dexamethasone (SerDex) in Pre-Reflex-oDST group. (A) Comparison of post-oDST SerCort and SerDex for no CS patients in the Pre-Reflex-oDST group. SerCort in the No CS patients stratified by the ARUP Lower limit of the reference range for SerDex (140 ng/dL). There was no significant difference in median SerCort with the SerDex <140 ng/dL (N = 20) and >140 ng/dL (N = 203) groups (1.2 vs 1.1 mcg/dL, respectively, P = 0.621). (B) Comparison of all Pre-Reflex-oDST group oDSTs stratified by patients with (blue) and without (red) CS. The black vertical solid line represents the limit of quantitation (LOQ) of SerDex (50 ng/dL). There was no correlation of SerDex and SerCort achieved in either group (see text for specifics). There was no correlation when NNH cases were removed as well (P = 0.432). CS = Cushing Syndrome; NH = neoplastic hypercortisolism; NNH = nonneoplastic hypercortisolism; oDST = overnight dexamethasone suppression test; SerDex = serum dexamethasone.

Discussion

The purpose of this study was to assess the usefulness of implementing a protocol to only reflex samples for the measurement of SerDex that do not suppress post-oDST SerCort (the “Reflex-oDST”) using a very conservative 8 AM cortisol cutoff. The major findings were as follows: (a) There was no detrimental effect on oDST-suppressed SerCort levels with the implementation of Reflex testing. That is, the SerCort levels in patients without CS were not different from each other Pre- and Post-Reflex-oDST. The same was found in the group who had CS. (b) There were comparable optimal SerCort ROC cutoff values in the Pre- and Post-Reflex-oDST groups, which also demonstrated a lack of a detrimental effect on test performance. (c) The Reflex protocol eliminated the need for SerDex measurement in 68% of oDSTs ordered without reducing the accuracy of the oDST. (d) No correlation was found between SerCort and SerDex indicating that the SerDex concentration achieved may not be an important factor in assessing the accuracy of the oDST; rather the presence of a detectible SerDex may be sufficient (ie, a Boolean function).
When comparing the Pre- and Post-Reflex-oDST groups, we observed no difference in patient population characteristics, including the prevalence of positive oDSTs, CS diagnosis, and CS etiology. Notably, patients who had CS were older than those who did not have CS in both groups. Ueland et al demonstrated a positive correlation between age and oDST SerCort, which may partially explain the significantly higher age in patients with CS.17 Age-related changes in HPA axis dynamics likely contributed to an increased prevalence of unsuppressed results.21 Additionally, older patients often have more comorbidities, which may lead clinicians to have a lower threshold for further evaluation, increasing the likelihood of identifying CS in this population.
To demonstrate that implementation of oDST Reflex protocol did not negatively affect diagnostic performance, we compared SerCort levels and false positive rates defined by unsuppressed SerCort later determined not to have CS through further testing. We found no difference in SerCort levels before and after implementation of Reflex testing (within the patients who did not have CS and within the patients who had CS). We observed a 7% false positive rate in the Pre-Reflex-oDST group that was comparable to 10% to 14% in previous studies.17,22 We found a comparable 9% false positive rate in the Post-Reflex-oDST group demonstrating preservation of test performance with Reflex implementation. These data are similar to those theorized by Genere et al18 and we have now validated the approach.
Implementation of reflex SerDex testing reduced the number of oDST SerDex measurements by ∼68% and resulted in a cost savings of $18.64 per ordered oDST using Medicare Clinical Diagnostic Laboratory Test reimbursement data, though this likely underestimates the true financial burden as patients are often billed at higher rates.20 Therefore, the Reflex protocol not only did not have a detrimental effect on test performance but also improved efficiency by reducing unnecessary costs and resource utilization. It is also important to point out that the approach is likely to save additional costs like avoiding additional analysis such as unnecessary plasma ACTH, salivary cortisols, UFCs, and even MRIs.
For the purposes of diagnosis of CS, we used accepted oDST SerCort cutoff of ≤1.8 mcg/dL (50 nmol/L) that yields a sensitivity of 95% and a specificity of ∼80%.10,12 We, like most clinicians, utilize a ≤1.8 mcg/dL SerCort diagnostic cutoff with concomitant measurement of SerDex to improve specificity by reducing false positives due to subtherapeutic dexamethasone levels. For the current study, we used the cutoff of 1.6 mcg/dL to determine when to reflex samples for SerDex in the Post-Reflex-oDST group to be as conservative as possible particularly when considering biological variability around a value of 1.8 mcg/dL.
To demonstrate equivalency, we found SerCort cutoff values that maximize specificity based on oDSTs performed similarly in both Pre- and Post-Reflex-oDST groups. Our calculated cutoff value for SerCort Pre- and Post-Reflex-oDST validated that a small increase in SerCort oDST cutoffs results in an increase in specificity to >95% (utilizing Youden’s index). However, given that the oDST is a screening test, sensitivity should be prioritized. While higher specificity reduces false positives, it may also increase the risk of missing mild CS cases. Notably, it has been shown that concomitant SerDex measurement reduces false positives by 20%,17 reinforcing the benefit of its inclusion.
To be conservative, we reanalyzed all of the data excluding the 6 patients with NNH. This had no effect on any of the outcomes. In fact, the oDST 8AM cortisol was almost identical when comparing NH to NNH patients further emphasizing the clinical challenge of distinguishing these highly overlapping groups in terms of their laboratory results.
Similar to previous studies, we found a broad range of SerDex levels across all oDSTs with minimal or no correlation to SerCort.9,23,24 To maximize specificity, Ueland et al proposed a SerDex cutoff value of 130 ng/dL [0.130 mcg/dL (3.3 nmol/L)], while Ceccato et al proposed a SerDex cutoff of 180 ng/dL [0.180 mcg/dL (4.5 nmol/L)] prioritizing specificity.17,25 SerCort levels the morning after taking 1 mg of dexamethasone (8 AM–9 AM) reflects delayed glucocorticoid negative feedback at the pituitary and hypothalamus that takes at least 1-2 h to be fully expressed.26 Therefore, differences in measured SerDex at 8 AM the morning after the 1 mg dose ingestion reflect the variability of HPA axis feedback sensitivity and the timing of the pharmacokinetics of dexamethasone metabolism that can be influenced by several factors, such as age, BMI, and concomitant medications.11,13,27,28 Our findings suggest that any detectible SerDex level (>50 ng/dL in our study), even if below the established reference interval (eg,140–295 ng/dL), is sufficient for a valid test and probably does not require repetition. That said, it may still be prudent to repeat the test if the SerCort does not suppress to <1.8 mcg/dL and the SerDex is < 100 ng/dL particularly with a high index of suspicion for CS.24 oDSTs with SerDex values below the laboratory’s detectable limits (LOQ) should still be considered invalid, most likely due to dexamethasone noncompliance or differences in absorption and/or pharmacokinetics as described above. It is also important to point out that the LOQ for some serum dexamethasone assays are higher than the assay we used, which makes this point even more important.18
An important final point is the practicability of the approach. Why not just store the serum cortisol sample and only test it for serum dexamethasone if requested18? This is very challenging for clinicians in practice who work with a variety of reference laboratories and are often not aware of the SerCort oDST results until after the sample has been discarded. By building the reflex approach into the ordering system, this problem is avoided as it does not require the intervention of the ordering clinician, thereby reducing the administrative burden while reducing laboratory costs. The significance of our novel study is confirmed by the fact that, subsequent to our implementation, a major reference laboratory has recently established a similar Reflex oDST test (https://www.labcorp.com/tests/503990/cortisol-dexamethasone-suppression-test-with-reflex-to-dexamethasone). Others are likely to follow. Our study, which is the first of its kind to our knowledge, should give the clinician assurance that this approach is appropriate. At our relatively small laboratory, this results in annual cost savings of $11,500 per year just for the dexamethasone levels not needed. The savings for each institutional and provider would obviously be different depending on their patient mix and test volumes.

Conclusion

We demonstrated that the implementation of the Reflex protocol avoided unnecessary SerDex measurements without affecting test performance, highlighting its utility from both a resource and cost standpoint. Additionally, our findings suggest that any quantifiable SerDex level, even if below the established reference interval, does not invalidate the oDST.

Disclosure

Dr Carroll is an Editorial Board Member of this journal and was not involved in the editorial review or the decision to publish this article. Dr Nerenz receives research funding from Abbott Laboratories.

Acknowledgment

The authors thank the personnel at Wisconsin Diagnostic Laboratories for their work to develop and implement the Reflex Testing protocol. J.D.K. is a recipient of the 2024 Research Experience for Graduate and Medical Students (REGMS) award from the Endocrine Society (US).

References

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