Endocrine Abstracts

Background: Overnight dexamethasone suppression tests (ONDST) are conducted to investigate patients with symptoms suggestive of cortisol hypersecretion or if an adrenal incidentaloma is identified. Cortisol levels of 50 nmol/l and above following ONDST may be related to autonomous cortisol secretion (ACS) and require further investigation. Determining likely presence of ACS is essential given reported associations with type 2 diabetes mellitus (T2DM), obesity, cardiovascular disease and osteoporosis. ONDST are inherently prone to interference and false positive rates are high, often resulting in clinicians conducting multiple ONDST, with associated patient and service impacts. Our study assesses the outcomes from a large UK cohort who underwent ONDST.

Methods: 560 unselected patients who underwent ONDST were retrospectively examined. Data were collected on indication, demographics including body mass index (BMI), biochemical results and co-morbidities. A positive ONDST was considered any cortisol greater than or equal to 50nmol/l, further categorised into mild ACS (MACS) between 50-138nmol/l and probable ACS >138nmol/l. Statistical analysis was conducted using Prism v9.3.1.

Results: 62% of the cohort were female. Mean age was 57.3 years ±17.1 (SD). Mean BMI was 30.5kg/m² ± 7.2. 71.6% had an adrenal lesion as the indication for the test, with a further 16.3% undergoing ONDST for clinical suspicion. 28% had an unsuppressed cortisol on ONDST (greater than or equal to 50nmol/l), of these 6.1% were greater than 138nmol/l. 48% of patients with an unsuppressed ONDST underwent repeat testing with 90.7% of results remaining unsuppressed. 47 patients with unsuppressed ONDST had an ACTH level recorded, 25.5% had an ACTH less than 5ng/l (normal range 5-47ng/l). 89.8% had a HbA1c recorded, with 31.2% having a result greater than 48mmol/mol or known T2DM. BMI did not correlate with suppressed vs unsuppressed cortisol on ONDST. Of the 157 patients with an unsuppressed cortisol, 63.7% had a potential confounder including obesity, diabetes or depression.

Conclusion: Our data demonstrates that there are high rates of unsuppressed cortisol following ONDST. Given the large numbers of patients with adrenal incidentalomas now identified and assessed, this leads to significant increased demand on endocrinology outpatient appointments. We have also shown that repeated ONDST may be unnecessary given greater than 90% remained unchanged, and the majority of patients had a potentially irreversible confounder. Therefore, we would suggest that careful further evaluation of the likelihood of MACS following a positive ONDST, through additional biochemical and clinical investigation but without a repeat ONDST, is required prior to any clinic attendance.