Saliva versus serum cortisol to identify subclinical hypercortisolism in adrenal incidentalomas: simplicity versus accuracy.

Purpose: Subclinical hypercortisolism (SCH) leads to metabolic derangements and increased cardiovascular risk. Cortisol autonomy is defined by the overnight 1 mg dexamethasone suppression test (DST). Saliva cortisol is an easier, stress-free, and cost-effective alternative to serum cortisol. We compared 23 h and post-1 mg DST saliva with serum cortisol to identify SCH in adrenal incidentalomas (AI).

Methods: We analyzed 359 DST obtained retrospectively from 226 AI subjects (173F/53 M; 19-83 years) for saliva and serum cortisol. We used three post-DST serum cortisol cutoffs to uncover SCH: 1.8, 2.5, and 5.0 μg/dL. We determined post-DST and 23 h saliva cortisol cutoffs by ROC curve analysis and calculated their sensitivities (S) and specificities (E).

Results: The sensitive 1.8 μg/dL cutoff defined 137 SCH and 180 non-functioning adenomas (NFA): post-DST and 23 h saliva cortisol S/E were: 75.2%/74.4% and 59.5%/65.9%, respectively. Using the specific 5.0 μg/dL cortisol cutoff (22 SCH/295 NFA), post-DST and 23 h saliva cortisol S/E were 86.4%/83.4% and 66.7%/80.4%, respectively. Using the intermediate 2.5 μg/dL cutoff (89 SCH/228 NFA), post-DST and 23 h saliva cortisol S/E were 80.9%/68.9% and 65.5%/62.8%, respectively.

Conclusion: Saliva cortisol showed acceptable performance only with the 5.0 μg/dL cortisol cutoff, as in overt Cushing's syndrome. Lower cutoffs (1.8 and 2.5 μg/dL) that identify larger samples of patients with poor metabolic outcomes are less accurate for screening. These results may be attributed to pre-analytical factors and inherent patient conditions. Thus, saliva cortisol cannot replace serum cortisol to identify SCH among patients with AI for screening DST.