Out-patient screening for Cushing's syndrome: The sensitivity of the combination of circadian rhythm and overnight dexamethasone suppression salivarycortisol tests

Screening tests have been used to support a biochemical diagnosis of Gushin g's syndrome (CS). Measurements of salivary cortisol offer facilities for s tudying out-patients. This study assessed salivary cortisol in screening fo r CS by evaluating hypercortisolism based on circadian rhythm and the overn ight 1-mg dexamethasone (DEX) suppression test for out-patients. We evaluat ed 33 patients with CS. Thirty normal volunteers and 18 obese patients were used as controls. Salivary cortisol (nanograms per dL) levels (mean +/- se al) were 596 +/- 44, 528 +/- 104, and 1205 +/- 118 (0900 h); 213 +/- 27, 32 5 +/- 76, and 778 +/- 74 (1700 h); and 95 +/- 8, 133 +/- 26, and 914 +/- 94 (2300 h) in normal controls, obese subjects, and CS patients, respectively . After the over night 1-mg DEX test, they were 64 +/- 1.1, 107 +/- 25, and 1048 +/- 129, respectively. In the present series, a single out-patient 09 00, 1700, and 2300 h measurement and an overnight 1-mg DEX salivary cortiso l level above the 90th percentile of the control or obese group values had sensitivities of 65.6%, 81.8%, 100%, and 100% or 78.1%, 57.6%, 93.3%, and 9 1.4%, respectively The sensitivity improved (100%) in response to the combi nation of 2300 h and overnight 1-mg DEX salivary cortisol suppression tests to differentiate between obese and CS subjects. Our data indicate that nig httime sample and overnight 1-mg DEX suppression salivary cortisol tests ar e sensitive markers for the diagnosis of CS. In addition, the combination o f the two tests improves the ability to differentiate between obese and CS patients and may be useful for out-patient screening.