Sensitivity of static and dynamic assays in the confirmation of Cushing's syndrome

Cushing syndrome (CS) is a variable clinical entity. Latent forms became more prevalent due to the performance of hormonal and radiological diagnostic tools. A multicenter retrospective study including all patients followed in the Endocrinology & Diabetology departments of Fattouma Bourguiba Hospital-Monastir and Farhat Hached Hospital-Sousse between 1989–2021, with confirmed endogenous CS. Midnight serum cortisol was greater than 75 ng/mL in 93.8% of patients followed for ACTH-dependent CS and 25% of whom with ACTH-independent CS (sensitivity of 80%). The UFC was elevated in 87.8% of patients with ACTH-dependent CS and 75% of patients with ACTH-independent CS. The 30 patients who had overnight-dexamethasone-suppression test all had high cortisol levels (100% sensitivity) with an average level well above the threshold. Serum cortisol levels under the 2-day low-dose dexamethasone-suppression-test were above the threshold (100% sensitivity) with a median cortisol level of 130 ng/mL. Our results were similar to those published by Shih-Chen Tung and al. who reported a midnight cortisol level > 75 ng/mL in 97.4% of the population. For UFC, with an estimated sensitivity of 84.2% in diagnosing CS, our results were similar to those of the Taiwanese study, which noted a 24-hour-UFC above threshold in 87.5–91.7% [1] . The overnight-dexamethasone-suppression test is highly recommended for screening. Its sensitivity exceeds 95% but its specificity is 80%. The 2-day-low-dose dexamethasone suppression test is performant for the diagnosis of CS with a sensitivity of 91–98% and a specificity of 70–95% in the literature [2] .