Midnight salivary cortisol for the diagnosis of Cushing's syndrome in a Chinese population

Singapore Med J. 2019 Jul;60(7):359-363. doi: 10.11622/smedj.2018154. Epub 2018 Nov 29.

Abstract

Introduction: Cushing's syndrome is defined as chronic excess free cortisol in circulation. According to recent studies, midnight salivary cortisol is an accurate and non-stress method for screening and diagnosing Cushing's syndrome. However, there is limited data on midnight salivary cortisol for diagnosing Cushing's syndrome in the Chinese population.

Methods: Among 61 suspected Chinese patients, 48 patients were confirmed to have Cushing's syndrome. We evaluated the midnight salivary cortisol, midnight serum cortisol and 24-hour urine free cortisol excretion for diagnosis. Midnight salivary cortisol was collected from 21 healthy volunteers for control purposes.

Results: In the patient group, mean urine free cortisol excretion and midnight salivary cortisol levels were 296.50 ± 47.99 µg/day and 10.18 ± 1.29 ng/mL, respectively. Among the control group and normal participants, mean midnight salivary cortisol level was 0.53 ± 0.13 ng/mL and 0.50 ± 0.12 ng/mL, respectively. The cut-off value for midnight salivary cortisol was 1.7 ng/mL for diagnosing Cushing's syndrome, with a sensitivity of 98% and specificity of 100%. The diagnostic performance of midnight salivary cortisol (area under the curve [AUC] = 0.99) was superior to that of urine free cortisol (AUC = 0.89).

Conclusion: Our study confirmed the good diagnostic performance of midnight salivary cortisol for diagnosing Cushing's syndrome in a Chinese population. Correlation between midnight salivary cortisol and either urine free cortisol or midnight serum cortisol was good. Midnight salivary cortisol is a convenient and precise tool for diagnosing Cushing's syndrome and can be the screening test of choice for Chinese populations.

Keywords: Cushing’s disease; Cushing’s syndrome; midnight salivary cortisol; midnight serum cortisol; urine free cortisol.

MeSH terms

  • Adult
  • Case-Control Studies
  • Cushing Syndrome / diagnosis*
  • Humans
  • Hydrocortisone / analysis*
  • Hydrocortisone / blood
  • Hydrocortisone / urine
  • Saliva / chemistry*
  • Time Factors
  • Young Adult

Substances

  • Hydrocortisone