Diagnostic performance of salivary cortisol and serum osteocalcin measurements in patients with overt and subclinical Cushing's syndrome

▶ Automated electrochemiluminescence immunoassay for salivary cortisol measurements. ▶ Serum osteocalcin compared to other tests used for the diagnosis of overt CS. ▶ Serum osteocalcin negatively correlates with serum and salivary cortisol concentrations. The cut-off value for salivary cortisol measurement for the diagnosis of Cushing's syndrome (CS) may depend both on the severity of the disease and the composition of control group. Therefore, we examined the utility of midnight salivary cortisol measurements in patients who were evaluated for signs and symptoms of CS or because they had adrenal incidentalomas. Because serum osteocalcin (OC) is considered as a sensitive marker of hypercortisolism, we also investigated whether OC could have a role in the diagnosis of CS. Each of the 151 patients was included into one of the following groups: (A) overt CS ( n = 23), (B) subclinical CS ( n = 18), (C) inactive adrenal adenomas ( n = 40), (D) patients without HPA disturbances ( n = 70). Patients (C + D) were used as controls. Serum, salivary and urinary cortisol, and OC were measured by electrochemiluminescence immunoassay. Group A had suppressed OC as compared to both group B and group (C + D). Serum and salivary cortisol concentrations showed strong negative correlations with OC in patients with overt CS. The areas under the curves of salivary and serum cortisol at 24:00 h (0.9790 and 0.9940, respectively) serum cortisol after low dose dexamethasone test (0.9930) and OC (0.9220) obtained from ROC aanalysis for the diagnosis of overt CS were not statistically different. This study confirms the usefulness of midnight salivary cortisol measurements in the diagnosis of overt CS in the everyday endocrinological praxis. Our results suggest that OC may have a role in the diagnosis of overt CS.