SAT-372 Correlation of Serum Dexamethasone and Cortisol Concentrations Post Dexamethasone 1 Mg in the Overnight Dexamethasone Suppression Test in Patients with Unilateral and Bilateral Adrenal Incidentalomas

Background: The most common functional abnormality in adrenal incidentalomas (AI) is autonomous cortisol secretion. Most guidelines recommend a 1 mg overnight dexamethasone suppression test (ONDST) as a screening test for this abnormality. There is some evidence that simultaneous measurement of post dexamethasone serum dexamethasone (SD) with serum cortisol (SC) improves the accuracy of the ONDST. We have therefore been routinely measuring SD in our unit to ensure adequate concentrations when interpreting the results of this test. Aim: To measure the correlation between SD and SC concentrations and SD with the decrement in serum cortisol levels from baseline (9 am the day before the test) to the post dexamethasone level (DSC) in the ONDST. Method: We examined the results of 57 patients with unilateral or bilateral adrenal incidentalomas who underwent a 1 mg ONDST on our unit. Using linear regression analysis, we correlated SC and SD concentrations and serum SD concentration with the DSC. We also examined whether lower levels of SD were associated with adequate suppression of SC following ONDST. Results: SD levels range 16, median 7.656 nmol/L. SC range