Endocrine Abstracts

JOINT964

Introduction: The overnight 1 mg dexamethasone suppression test (ODST) is used to screen and diagnose Cushing’s syndrome, suspected when plasma cortisol levels exceed 1.8 μg/dl after dexamethasone administration. However, factors such as stress, illness, obesity, pregnancy, oral contraceptives, alcohol abuse, depression, and medications affecting dexamethasone metabolism can lead to false-positive results, requiring careful interpretation. This study aims to propose new criteria for ODST cortisol levels in diagnosing Cushing’s syndrome by confirming whether patients with positive ODST results were diagnosed with Cushing’s syndrome through further testing.

Methods: This study was conducted on subjects who showed positive results from ODST for the evaluation of adrenal adenoma or adrenal hyperplasia and subsequently underwent the low dose dexamethasone suppression test (LDDST) between January 2021 and October 2024 at Kangbuk Samusng Hospital. Patients with CKD grade 3b (estimated glomerular filtration rate [eGFR] < 45 ml/min/1.73m²), those on medications affecting dexamethasone metabolism, and those undergoing cancer treatment were excluded. Diagnosis of Cushing’s syndrome required two or more positive results from the ODST, LDDST, or late-night serum cortisol test (> 7.5 μg/dl).

Results: A total of 154 patients with positive ODST results underwent the LDDST. The mean age of the subjects was 55.9 ± 14.2 years, 58 (37.7%) were male, and the median body mass index (BMI) was 24.7 [22.7, 27.3] kg/m². 73 (47.4%) had hypertension, 37 (24.0%) had diabetes, and 46 (29.9%) had dyslipidemia. The median eGFR was 101.1 ml/min/1.73m². The basal, ODST, LDDST, and late-night cortisol levels were 11.4, 3.5, 2.8, and 4.6 μg/dl, respectively. Among the patients, 42 were not diagnosed with Cushing’s syndrome, while 112 were. There were no significant differences in age, BMI, sex, or comorbidities between those diagnosed and those not diagnosed with Cushing’s syndrome. The eGFR was significantly lower in patients without Cushing’s syndrome (97.0 [87.9, 104.6] ml/min/1.73m²) compared to those with Cushing’s syndrome (102.5 [94.3, 110.9] ml/min/1.73m²) (P = 0.039). ODST, LDDST, and late-night cortisol levels were significantly lower in patients without Cushing’s syndrome (P < 0.001). The ODST cortisol level for diagnosing Cushing’s syndrome was 3.15 μg/dl (AUC 0.818).

Conclusion: Despite positive ODST results, many patients were not diagnosed with Cushing’s syndrome. Considering the high prevalence of obesity and stress in modern society, further research is needed to establish new criteria for ODST cortisol levels in diagnosing Cushing’s syndrome.