FRI172 Assessment Of Plasma Dexamethasone Levels After 1-mg Dexamethasone Suppression Test In Adults With Obesity

Disclosure: P. Paopongpaiboon: None. P. Santisitthanon: None. N. Houngngam: None. T. Snabboon: None. P. Boonchaya-anant: None. Background: The 1-mg overnight dexamethasone suppression test is the most frequently used screening test for Cushing’s syndrome. It has been proposed that obese patients may have insufficient plasma dexamethasone levels for the test which may result in false positives. We sought to compare the plasma dexamethasone levels after 1-mg DST in healthy obese participants and in normal-weight participants. Methods: A total of 30 normal-weight participants (BMI ≤ 25 kg/m(2)) and 62 obese participants (BMI >25 kg/m(2)) were enrolled in the study. Obese patients were further divided into class 1 (25 - 29.9 kg/m(2)) and class 2 (>30 kg/m(2)). After a standard overnight 1-mg dexamethasone suppression test, blood samples were obtained for serum cortisol and plasma dexamethasone levels. Plasma dexamethasone levels were quantified using liquid chromatography - mass spectrometry (LC-MS/MS). Results: No significant difference in plasma dexamethasone levels were found between obese and normal-weight participants (3.31 ± 1.35 vs 2.82 ± 1.11 nmol/L, mean ± SD; P=0.09 respectively). There were also no correlations found between sex, BMI, body surface area (BSA) and plasma dexamethasone levels. There was also no significant difference in the proportion of participants who achieved a plasma dexamethasone level > 3.3 nmol/L in comparison between obesity class 1, obesity class 2, and normal-weight groups. Conclusion: We did not find a difference in plasma dexamethasone levels after 1-mg DST between obese and normal-weight participants. Our results suggest that BMI does not affect plasma dexamethasone levels and routine dexamethasone measurement may not help to identify false-positives using the 1-mg DST. Presentation: Friday, June 16, 2023