Salivary cortisol and cortisone in diagnosis of Cushing's syndrome- a comparison of six different analytical methods.

Abstract

Salivary cortisol and cortisone at late night and after dexamethasone suppression test (DST) are increasingly used for screening of Cushing's syndrome (CS). We aimed to establish reference intervals for salivary cortisol and cortisone with three liquid chromatography-tandem mass spectrometry (LC-MS/MS) techniques and for salivary cortisol with three immunoassays (IAs), and evaluate their diagnostic accuracy for CS. Salivary samples at 08:00h, 23:00h and 08:00h after a 1-mg DST were collected from a reference population (n=155) and patients with CS (n=22). Sample aliquots were analyzed by three LC-MS/MS and three IA methods. After establishing reference intervals, the upper reference limit (URL) for each method was used to calculate sensitivity and specificity for CS. Diagnostic accuracy was evaluated by comparing ROC curves. URLs for salivary cortisol at 23:00h were similar for the LC-MS/MS methods (3.4-3.9nmol/L), but varied between IAs: Roche (5.8nmol/L), Salimetrics (4.3nmol/L), Cisbio (21.6nmol/L). Corresponding URLs after DST were 0.7-1.0, and 2.4, 4.0 and 5.4nmol/L, respectively. Salivary cortisone URLs were 13.5-16.6nmol/L at 23:00h and 3.0-3.5nmol/L at 08:00h after DST. All methods had ROC AUCs≥0.96. We present robust reference intervals for salivary cortisol and cortisone at 08:00h, 23:00h and 08:00h after DST for several clinically used methods. The similarities between LC-MS/MS methods allows for direct comparison of absolute values. Diagnostic accuracy for CS was high for all salivary cortisol and cortisone LC-MS/MS methods and salivary cortisol IAs evaluated.