The aim of the present study is to evaluate the measurement of midnight salivary cortisol as a method of screening for Cushing’s syndrome (CS). Here we tested the performance of a highly sensitive electrochemiluminescence immunoassay (ECLIA) for midnight salivary cortisol measurement in an extensive clinical study (n=104). Three groups were investigated: 30 patients with CS, 34 with obesity and 40 healthy normal weight controls. All of them collected saliva samples at 24:00 h and urine samples over the same day (24 hour period). An electrochemiluminescence immunoassay was used to measure salivary cortisol. Mean midnight salivary cortisol in healthy volunteers, obese patients and patients with CS was 8.33 ± 3.62, 8.13 ± 4.47 and 33.11 ± 21.68 nmol/l, respectively. No significant difference was found between midnight salivary cortisol in healthy and obese subjects (P>0.05). In contrast, salivary cortisol at midnight was significantly higher in patients with CS (P<0.001) as compared to both other groups. The cut-off point of 14.2 nmol/l yielded a sensitivity of 93.3% and a specificity of 94.2% (AUCROC=0.984 ± 0.01(0.965-1.000). A strong positive correlation between midnight salivary cortisol and urinary free cortisol has been found in the CS group (r=0.686, P<0.0001). Our results demonstrate that measurement of midnight salivary cortisol could be successfully used as a first-line screening method for CS. Our data approve ECLIA as a simple, reliable and timesaving method for the assessment of salivary cortisol. Automated measurement of midnight salivary cortisol by ECLIA would facilitate the routine practice in the screening for CS.
Financed by the National Centre for Research and Development under grant No. SP/I/1/77065/10 by the strategic scientific research and experimental development program:
SYNAT - “Interdisciplinary System for Interactive Scientific and Scientific-Technical Information”.