Diagnostic performance of late-night salivary cortisol measured by automated electrochemiluminescence immunoassay in obese and overweight patients referred to exclude Cushing’s syndrome

Abstract

This study estimates diagnostic performance of late-night salivary cortisol (LNSC) as measured by automated electrochemiluminescence immunoassay (ECLIA), evaluates the clinical implication of two consecutive LNSC measurements, and compares its accuracy with enzyme-linked immunosorbent assay (ELISA) and serum cortisol after low-dose dexamethasone suppression test (DST) in obese and overweight patients referred for suspected Cushing's syndrome (CS). One hundred twenty three consecutive obese and overweight referred patients and 98 healthy volunteers provided two saliva samples collected at 23:00 using a Salivette (Sarstedt, Germany), assayed by ECLIA (Cobas e601) and ELISA. The patients underwent DST and were further evaluated until CS was pathologically confirmed (n = 45) or excluded. Diagnostic performance of LNSC was evaluated by receiver operating characteristic (ROC) analysis. The total areas under the curve (AUC) were calculated to compare the different tests. We found that a cut-off value of 9.4 nmol/l can differentiate CS among obese and overweight patients with sensitivity of 84.4 % (95% CI 71.2-92.2), specificity of 92.3 % (95% CI 84.2-96.4), and diagnostic odds ratio of 65.1 (95% CI 20.4-207.6). No difference was found between AUCs from the first, second, and the mean from the two LNSC measurements (ECLIA), LNSC (ELISA), or DST. The single LNSC (ECLIA) and DST improved the sensitivity and specificity for concordant results up to 100 and 97.4 %, respectively. In conclusion, due to its automation and its comparable diagnostic performance, ECLIA is preferable as a first-line LNSC screening test for CS. The initial use of single LNSC followed by DST provides better diagnostic performance for concordant results.

Salivary cortisol and the diagnosis of Cushing’s syndrome: a coming of age

“…The study by Belaya et al [5] appearing in this journal confirms prior studies that the measurement of LNSC can be performed by a widely available platform immunoassay. Considering the simplicity of obtaining an LNSC sample and the availability of the measurement by platform immunoassay, there should be no barrier to any clinician obtaining this screening test even with a modest degree of suspicion of Cushing's syndrome.…”

“…It is not uncommon for one of the samples to have insufficient quantity of saliva for analysis even with our extraordinarily sensitive ELISA that requires only 25 lL of saliva per well [8]. In fact, one piece of information apparently not included in Belaya et al [5] or Carrasco et al [7] is the volume of saliva necessary for the automated immunoassay, although a study using a similar automated immunoassay stated that only 20 lL of saliva is necessary [9]. Regardless, since the saliva sampling is done at home and we receive samples from across the US, we find it prudent to obtain two samples in case one has inadequate volume or some other problem with sample integrity.…”

“…Since the overnight dexamethasone suppression test combined with LNSC improved the overall specificity, as demonstrated previously [10], the authors may be correct. (3) One problem not mentioned by Belaya et al [5] or Carrasco et al [7] is the potential for contamination of the saliva sample with cross-reacting topical corticosteroids if and when the sampling is done by the subject at home [11]. It may be that over-thecounter hydrocortisone creams and ointments (containing authentic cortisol) are not widely available or used in Russia or Chile.…”

Diagnostic performance of osteocalcin measurements in patients with endogenous Cushing’s syndrome

“…19 The initial use of LNSC measured by ECLIA (reference range 0.5-9.4 nmol l À 1 ) 20 was independently followed by DST (cutoff value forsuppression: 50 nmol l À 1 ). 19 Any patients with discordant results from the initial evaluations underwent an additional third or fourth test: 24hUFC (reference range 60-413 nmol per 24 h) and/or awake serum cortisol at 2300 hours (reference range 46-270 nmol l À 1 ).…”

“…17 However, the most challenging cases involve differentiating patients with endogenous CS from obese subjects due to similar clinical features and complications such as the presence of functional hypercortisolism with relatively higher cortisol levels in obese subjects compared with healthy controls. [18][19][20] Furthermore, elderly patients with CS usually do not show typical changes in their appearance, and many of these patients remain undiagnosed, receiving treatment for hypertension, diabetes and osteoporosis. An active screening for CS among 219 consecutive patients (200 women and 19 men) referred for treatment of osteoporosis revealed the prevalence of subclinical CS in 4.8% of subjects.…”