Impaired accuracy of the dexamethasone suppression test after bariatric surgery: implications for post-surgical cortisol interpretation

BACKGROUND: The impact of bariatric surgery (BS) on the performance of 1mg Dexamethasone suppression test (DST) is not well established. OBJECTIVE: (1) To evaluate the intraindividual results of the DST in a group of patients before and 2 years after BS, and (2) to assess plasma dexamethasone levels and other factors influencing the reliability of the DST. METHODS: We conducted a prospective longitudinal study including 38 subjects evaluating DST before and 2 years after BS. We also compared DST results, plasma dexamethasone levels, and related factors across three groups: individuals of the previous cohort two years post-BS (n= 21), patients with severe obesity without BS (pwO) (n= 10), and healthy controls (n= 7). RESULTS: Post-BS patients had higher cortisol levels after DST compared to prior (0.9 vs. 0.7 µg/dL; p<0.01). Four individuals post-BS had cortisol levels >1.8 µg/dL in absence of autonomous cortisol secretion. Plasma dexamethasone levels were significantly lower in post-BS patients (1.9 ng/dL) compared to non-operated pwO (3.7 ng/dL) and healthy controls (4.0 ng/mL), p<0.01. Multivariate analysis identified BS (β= -1.258, p= 0.01) and SHBG levels (β= -0.013, p= 0.04) as significant independent predictors of plasma dexamethasone concentrations. CONCLUSION: Post-BS subjects showed higher post-DST cortisol levels and reached lower plasma dexamethasone concentration compared to non-operated individuals, which may lead to false-positive results. These findings highlight the need to consider dexamethasone measurements to enhance DST interpretation in post-BS patients. Further studies are necessary to validate these findings in broader populations. The underlying mechanisms need to be explored.