Validation of Salivary Cortisol among Filipino Adults Suspected with Cushing's Syndrome

Tom Edward No. Lo, Queenie G. Ngalob, Margarita Victoria Holgado-Galicia and
Frances Lina Lantion-Ang

Section of Endocrinology, Diabetes and Metabolism, Department of Medicine,
College of Medicine and Philippine General Hospital, University of the Philippines Manila

Background. Cushing's syndrome is a state of hypercortisolism manifesting non-specific clinical features where its diagnosis entails biochemical confirmation of cortisol excess. This study aims to validate the efficacy of midnight salivary cortisol as a screening test for Filipinos suspected with Cushing's syndrome and determine the cut-off value applicable in the local setting.

Methods. This is a cross-sectional study of Filipinos suspected with endogenous Cushing's syndrome seen at a tertiary hospital. Modifcation of plasma costisol measured by RIA was used to predictive value, negative predictive value and area under the curve of the screening tests were estimated and compared using 48 hour low dose dexamethasone suppression test (LDDST) as the reference standard.

Results. The determined cut-off value (>= 7.0 nmol/L) for salivary cortisol showed a relatively high sensitivity (91.3%) and specificity (89.5%) in detecting cases suspected of Cushing's syndrome.  One milligram (1 mg) dexamethasone suppression test had the highest sensitivity (100%) but had the lowest specificity (68.4%) as a screening test. The area under the curve of the three diagnostic tests appeared to be similar when compared with the low dose dexamethasone suppression test.

Conclusion. Using a cut-off value of 7 nmol/L, local utility of late-night salivary cortisol has a high sensitivity and specificity in detecting Cushing's syndrome. It has a similar efficiency with 24-hour urine free cortisol and 1mg dexamethasone suppression test as a screening test for Cushing's syndrome. Salivary cortisol may be considered as a valid initial screening test for Filipinos suspected of Cushing's syndrome.

Key Words: salivary cortisol, Cushing's syndrome, serum cortisol, dexamethasone suppression test