Determination of cortisol cut-off limits in the overnight dexamethason suppression test using roche elecsys® cortisol II immunoassay

Nanna Thurmann Jorgensen; Stina Willemoes Borresen; Linda Hilsted; Kasper Brodbaek; Randi Ugleholdt; Claus Feltoft; Ulla Feldt-Rasmussen; Marianne Klose

doi:10.1530/endoabs.110.P132

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Endocrine Abstracts (2025) 110 P132 | DOI: 10.1530/endoabs.110.P132

ECEESPE2025 Poster Presentations Adrenal and Cardiovascular Endocrinology (169 abstracts)

Determination of cortisol cut-off limits in the overnight dexamethason suppression test using roche elecsys® cortisol II immunoassay

Nanna Thurmann Jørgensen ¹ , Stina Willemoes Borresen ¹ , Linda Hilsted ² , Kasper Brødbæk ² , Randi Ugleholdt ³ , Claus Feltoft ³ , Ulla Feldt-Rasmussen ¹ & Marianne Klose ¹

Author affiliations

¹Copenhagen University Hospital, Rigshospitalet, Department of Kidney and Hormone Diseases, Copenhagen, Denmark; ²Copenhagen University Hospital, Rigshospitalet, Department of Clinical Biochemistry, Copenhagen, Denmark; ³Copenhagen University Hospital, Herlev, Department of Medicine, Copenhagen, Denmark

JOINT2739

Background and aim: Mild autonomous cortisol secretion (MACS) is defined as excessive cortisol secretion but without the clinical phenotype of Cushing’s syndrome in the context of an adrenal incidentaloma. Still, MACS has been associated with increased mortality and risk of type 2 diabetes, hypertension, obesity, and osteoporosis. Diagnostic tests capable of detecting MACS are lacking, but cortisol concentrations in plasma after a 1 mg overnight dexamethasone suppression test (1 mg DST) has the highest sensitivity of available biochemical analyses. A cut-off of 50 nmol/l has been recommended in the recent guidelines from ESE/ENS@T, but as measurement of cortisol concentrations is method dependent, this study aimed to establish the assay-specific cut-off of the 1 mg DST using the Roche Elecsys^® Cortisol II immunoassay (ElecsysCortII) in a cohort of patients with adrenal incidentalomas.

Methods: Healthy participants (n=101, 57 women, median [range] age 60 [19–81] years) and patients with incidentalomas (n=106, 56 women, median [range] age 63 [40–85] years) underwent a 1 mg DST (dexamethason was taken between 2300 and 2400 h, and blood samples were collected between 0800 and 0900 h the following day) with plasma cortisol samples analyzed using ElecsysCortII. Cut-off limit for a normal response to the 1 mg DST was defined as the 97.5th percentile in the healthy participants.

Results: Two healthy participants were referred to the endocrinology department due to high 1 mg DST plasma cortisol levels (336 and 415 nmol/l, respectively), and thus excluded from the analyses. In the remaining healthy participants, the 0800 to 0900 h cortisol cut-off limit for the 1 mg DST was 68.9 [CI 63.1–75.3] nmol/l (ElecsysCortII). Forty-four percent of patients with an incidentaloma had a 1 mg DST cortisol above the recommended cut-off of 50 nmol/l, whereas 15% had a cortisol concentration above the assay-specific cut-off of 68.9 nmol/l.

Conclusion: ElecsysCortII-specific cortisol cut-off in healthy participants demonstrated a higher cut-off compared with previous recommendation of 50 nmol/l, and fewer than half as many patients exceeded the cut-off 68.9 nmol/l. As the number of referred patients suspected of MACS depends on the cut-off, the present findings may provide evidence for always adjusting the normal cut-off according to the local cortisol method.