Endocrine Abstracts

Introduction: The 1-mg overnight low-dose dexamethasone suppression test (DST) has been used to screen for mild autonomous cortisol secretion and Cushing’s syndrome (CS). The aim of the present study was to determine the DST discriminatory threshold confirming the diagnosis of CS.

Methods: This was a monocentric retrospective study including patients who were admitted to the Department of Endocrinology of La Rabta Hospital, Tunis between 2014 and 2023 for suspicion of CS. All patients underwent 1-mg DST followed by the 4-mg DST. A serum cortisol level <1.8 μg/dl at 08h after DST exclude the diagnosis of CS.

Results: One hundred two patients (69 women and 33 men) were enrolled in this study. Their mean age was 56.6 ± 14.7 years. The diagnosis of CS was confirmed in 63 patients (62%) and ruled out in 39 patients (38%). The mean serum cortisol level after the 1-mg DST was 7.4 ± 6.9 μg/dl in patients with CS and 4.4 ± 4.7 μg/dl in those without CS (P=0.019). It was 10.1 ± 8.8 µg/dl in patients with CS clinical features and 4.4 ± 3.3 µg/dl in patients without CS clinical features (P<0.001). The area under the ROC curve of serum cortisol level after the 1- mg DST was 0.726 (P<0.00). A cut-off value of 1.8 μg/dl had a sensitivity of 100% and a specificity of 10%. A cut-off value of 10 μg/dl was associated with the diagnosis of Cushing syndrome (Odds Ratio= 4.5, P=0.034) with a specificity of 95%. A cut-off value of 24 μg/dl confirmed the diagnosis of CS in 100% of cases.

Conclusion: This study provides evidence that with a higher cutoff for serum cortisol level as 24 µg/dl, the 1-mg DST establishes the diagnosis of CS without the need for other tests.