Objective: Late-night salivary cortisol (LNSC) is reportedly highly accurate for the diagnosis of Cushing's syndrome (CS). However, diagnostic thresholds for abnormal results are based on healthy, young populations and limited data are available on its use in elderly populations with chronic medical conditions. The purpose of this study was to evaluate LNSC levels in elderly male veterans with and without diabetes.
Design: Prospective evaluation of LNSC levels in male veterans.
Patients: One hundred and fifty-four participants with type 2 diabetes and 52 participants without diabetes.
Measurements: Participants underwent outpatient LNSC (2300 h) testing. Participants with elevated LNSC (> or = 4.3 nmol/l) underwent secondary testing, including 24-h urine free cortisol (24UFC, > 60 microg/day) and dexamethasone suppression testing (DST, serum cortisol > 50 nmol/l). Participants with positive secondary testing had a morning ACTH level analysed and either pituitary or adrenal imaging performed.
Results: One hundred and forty-one diabetics and 46 controls (mean age 61 years) returned samples (91% overall). Average LNSC levels (nmol/l) in diabetics were significantly higher than in nondiabetics [median (interquartile range): 2.6 (1.8-4.1) vs. 1.6 (1.0-2.0)] and in those aged > or = 60 compared to < 60 [2.7 (2.0-4.3) vs. 1.9 (1.4-2.9)] (P < 0.001 for both). Thirty-one participants required secondary testing. Seventy-nine per cent of participants who underwent secondary testing had normal 24UFC and DST. No cases of CS have been diagnosed to date. Increasing age [odds ratio (OR) 2.0 per decade], current diabetes mellitus (OR 4.4), and elevated blood pressure (OR 1.3 per 10 mmHg increase in systolic blood pressure) were associated with abnormal LNSC results (P < 0.05 for each).
Conclusions: LNSC has been shown to be sensitive and specific in diagnosing CS in certain high-risk populations, primarily the young and middle-aged. The development of age- and comorbidity-adjusted thresholds may be warranted for LNSC testing in elderly subjects and in those with significant comorbidity.