SFEBES2026 Poster Presentations Adrenal and Cardiovascular (54 abstracts)
Beyond the 50 nmol/l cut-off: improving 1 mg-overnight dexamethasone suppression test accuracy with assay-specific thresholds
Chiara Pilloni 1,2,3,4 , Laura Lewis 5 , Sumedha Mandal 1 , Giulia Lanzolla 3,4 , Miriam Asia 2 , Cristina L. Ronchi 1,2 , Francesco Boi 3,4 & Alessandro Prete 6,2,7
1Department of Metabolism and Systems Science, School of Medical Sciences, College of Medicine and Health, University of Birmingham, Birmingham, United Kingdom; 2Department of Endocrinology, Queen Elizabeth Hospital, University Hospitals Birmingham NHS Foundation Trust, Birmingham, Birmingham, United Kingdom; 3Endocrinology Unit, Department of Medical Science and Public Health, University of Cagliari, University Hospital of Cagliari, Cagliari, Italy; 4Endocrinology, Diabetology and Internal Medicine Unit, Catholic University of the Sacred Heart, Rome, Italy; 5Department of Biochemistry, Queen Elizabeth Hospital, University Hospitals Birmingham NHS Foundation Trust, Birmingham, United Kingdom; 6Department of Metabolism and Systems Science, School of Medical Sciences, College of Medicine and Health, University of Birmingham, Birmingham, Italy; 7National Institute for Health and Care Research (NIHR) Birmingham Biomedical Research Centre, Birmingham, Italy
Background: The 1 mg-overnight dexamethasone suppression test (1 mg-DST) is widely used to screen for autonomous cortisol secretion. Despite its simplicity, non-compliance and suboptimal dexamethasone exposure can affect its accuracy. Moreover, there is limited evidence on how different serum cortisol assays impact the commonly used 50 nmol/l cut-off.
Methods: All 1 mg-DST with immunoassay (IA; Abbott Alinity) serum cortisol >50 nmol/l measured at UHB NHS Foundation Trust between October 2018 and February 2025 had corresponding cortisol and dexamethasone levels assessed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). A dexamethasone cut-off ≥3.3 nmol/l defined adequate exposure. Linear regression, logistic regression, and Bland–Altman analyses compared IA and LC-MS/MS results.
Results: We analysed 521 1 mg-DST results from 437 patients; 46 (8.8%) had undetectable dexamethasone levels, suggesting non-compliance, and 45 (8.6%) had suboptimal levels. IA and LC-MS/MS cortisol measurements showed good agreement (R2 0.867; P < 0.001), but IA had a mean bias of -10.4 nmol/l. Cortisol correlated negatively with dexamethasone levels (R2 0.014; p 0.009), while dexamethasone correlated positively with age (R2 0.027; P < 0.001) and negatively with estimated glomerular filtration rate (R2 0.01; p 0.033). Multivariable logistic regression identified strong CYP3A4 inducer use as the only predictor of false-positive 1 mg-DST results (odds ratio 25.6, 95% confidence interval 9.3-77.6).
Conclusions: Routine dexamethasone measurement in abnormal 1 mg-DSTs identified a 17.4% false-positive rate. Careful drug history to exclude CYP3A4 inducers improves test accuracy. Despite good IA / LC-MS/MS agreement, IA shows negative bias; we propose a 40 nmol/l cut-off for IA Abbott Alinity to better detect autonomous cortisol secretion.
Volume 117
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Endocrine Abstracts
ISSN 1470-3947 (print) | ISSN 1479-6848 (online)
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