Cutoff Values of Late Night Salivary Cortisol for the Screening of Cushing's Syndrome Using an Automated Eclia
Posted: 16 Jun 2017
Date Written: June 15, 2017
The thresholds of late night salivary cortisol (LNSC) vary widely among studies due to differences in assay methodologies and in control groups.
We aimed in the present study to verify the analytical performance of the electro chimi luminesence assay (ECLIA) and to establish cutoff values of LNSC for the diagnosis of Cushing’s Sydrome (CS).
Methods: Patients with suspected CS underwent screening tests including an assessment of late night salivary cortisol and 1 mg overnight dexamethasone suppression test (DST), with measurement of serum cortisol. Subjects with abnormal response underwent a 2 mg DST, ACTH assessment and complementary radiological explorations. Serum and salivary cortisol were assessed by ECLIA. For the analytical evaluation, the study was performed with guidance from the Clinical and Laboratory Standards Institute (CLSI, formerly NCCLS).
Results: A total of 56 patients with mean age 57,7 years were finally enrolled. LNSC was correlated with nocturnal serum cortisol (r=0.56, p=0.004), with serum cortisol after 1 mg DST (r =0.82, p=0.04) and after 2 mg DST (r= 0.89, p<0.001, table II) but not with serum creatinine. BMI was correlated with serum cortisol after 1 mg DST but not with salivary cortisol .Using a 2.48 ng/ ml threshold derived from ROC analysis, the sensitivity and specificity of LNSC to identify CS was 84.6 % and 69.4 % respectively. The intra assay and inter assay coefficients of variation (CV) were 9.84 % and 10.5 % respectively. The detection and quantification limits for salivary cortisol measurement were 0.05 ng/ml (analytical sensitivity) and 0.08 ng/ml(functional sensitivity) respectively.
Conclusion: Our data confirm the usefulness of late night salivary cortisol measurement as an initial and simple test for screening for Cushing’s syndrome, for the first time in Tunisia using an automated ECLIA.
Keywords: Cushing’s syndrome; Corticosteroids; Cut off; Immunoassay; Saliva
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