Endocrine Abstracts

Introduction: Cushing’s syndrome is rare, but assessment of patients with clinical suspicion of Cushing’s and/or adrenal incidentaloma is frequently required. Thus, there is a need for biochemical screening methods that with high sensitivity and specificity identifies or rule out hypercortisolism. Analysis of late night salivary cortisol allows an easy sampling procedure performed at home and is independent of variations in plasma CBG levels. Analysis by liquid chromatography tandem mass spectrometry (LCMS) allows high analytical specificity and simultaneous analysis of salivary cortisol and cortisone, but robust reference limits and clinical cut-off levels are needed. Analysis of both cortisol and cortisone also allows quality control for contamination by blood or exogenous hydrocortisone.

Objective: Establishing solid reference intervals and clinical cut off levels for salivary cortisol and cortisone in the evening and after low dose dexamethasone suppression (LDDST) test using LCMS.

Methods: Salivary samples were collected at 0800, 2300 and at 0800 h after 1 mg dexamethasone from 175 reference subjects and 24 patients with Cushing syndrome using Salivette^® cortisol tubes. Half of the reference group also collected samples at 2000 and 2200. Salivary cortisol and cortisone was analysed with LCMS. Reference interval (2.5th and 97.5th percentile) was calculated non-parametrically and the best cut-off level for discrimination between Cushing patients and reference population was calculated using receiver operating characteristics analysis.

Results: The 97.5th percentile of the cortisol:cortisone ratio was 0.81. Samples with a ratio ≥1.0 was excluded from the reference samples for suspicion of contamination of blood or exogenous hydrocortisone. The reference range and cut-off levels for Cushing patients vs. reference population for salivary cortisol and cortisone are presented in the table below. There was no significant difference in salivary cortisol or cortisone at 2200 h compared with 2300 h, whereas the levels were were significantly higher at 2000 h.

Conclusion: A robust reference range for late night salivary cortisol and cortisone and after LDDST for the LCMS method was established. Patients with Cushing’s syndrome were separated from the reference population with high sensitivity and specificity and salivary cortisone appeared slightly superior to salivary cortisol. Late night samples may be collected at 2200–2300 h.