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

Importance: The impact of bariatric surgery (BS) on the performance of the 1 mg 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 3 groups: individuals of the previous cohort 2 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 with prior (0.9 vs 0.7 µg/dL; P < .01). Four individuals post-BS had cortisol levels >1.8 µg/dL in the absence of autonomous cortisol secretion. Plasma dexamethasone levels were significantly lower in post-BS patients (1.9 ng/dL) compared with non-operated pwO (3.7 ng/dL) and healthy controls (4.0 ng/mL), P < .01. Multivariate analysis identified BS (β = -1.258, P = .01) and sex hormone-binding globulin levels (β = -.013, P = .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 with 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.