Relationship between body mass index and 1 mg dexamethasone suppression test in patients with obesity

Abstract Aims The 1 mg dexamethasone suppression test (DST) shows variable results in obesity, yet the impact of extreme obesity (body mass index [BMI] ≥50 kg/m 2 ) on hypothalamic–pituitary–adrenal axis function remains poorly characterized. This study evaluated post‐dexamethasone cortisol levels across distinct BMI categories and their associations with metabolic parameters. Materials and Methods This retrospective study included 352 adults with obesity (BMI ≥30 kg/m 2 ) who underwent 1 mg overnight DST between February 2019 and August 2023. Patients were stratified into three groups: BMI 30.0–39.9 kg/m 2 ( n = 64), BMI 40.0–49.9 kg/m 2 ( n = 202), and BMI ≥50.0 kg/m 2 ( n = 86). Clinical, anthropometric, and laboratory parameters were compared between groups. Results The cohort had a median age of 41 years and comprised 284 females (80.7%). Post‐dexamethasone cortisol levels showed modest differences across BMI categories (median 0.79, 0.77, and 0.88 μg/dL, respectively; p = 0.038). Inadequate cortisol suppression after the 1 mg dexamethasone test was rare, occurring in four patients (1.1%) overall: 0/64 (0%) in BMI 30.0–39.9 kg/m 2 , 2/202 (1.0%) in BMI 40.0–49.9 kg/m 2 , and 2/86 (2.3%) in BMI ≥50.0 kg/m 2 ; continuous BMI was not associated with post‐dexamethasone cortisol levels. Patients with super obesity demonstrated higher rates of hypertension (36% vs. 18.7–22.2%, p = 0.021) and diabetes (30.2% vs. 16.8–18.7%, p = 0.033). Conclusions These findings emphasize that elevated post‐dexamethasone cortisol levels in patients with obesity should not be attributed to body weight alone but warrant appropriate evaluation for true hypercortisolism, with clinical interpretation guided by metabolic phenotype rather than BMI.