Reassessing the reliability of the salivary cortisol assay for the diagnosis of Cushing syndrome

Objective The cortisol concentration in saliva is 10-fold lower than total serum cortisol and accurately reflects the serum concentration, both levels being lowest around midnight. The salivary cortisol assay measures free cortisol and is unaffected by confounding factors. This study analysed published data on the sensitivity and specificity of salivary cortisol levels in the diagnosis of Cushing syndrome. Methods Data from studies on the use of different salivary cortisol assay techniques in the diagnosis of Cushing syndrome, published between 1998 and 2012 and retrieved using Ovid MEDLINE (R), were analysed for variance and correlation. Results For the 11 studies analysed, mean sensitivity and specificity of the salivary cortisol assay were both >90%. Repeated measurements were easily made with this assay, enabling improved diagnostic accuracy in comparison with total serum cortisol measurements. Conclusions This analysis confirms the reliability of the saliva cortisol assay as pragmatic tool for the accurate diagnosis of Cushing syndrome. With many countries reporting a rising prevalence of metabolic syndrome, diabetes and obesity - in which there is often a high circulating cortisol level - salivary cortisol measurement will help distinguish these states from Cushing syndrome.