BACKGROUND: The determination of Night Salivary Cortisol (NSC) is a useful survey in the screening for hypercortilosism. Study data about its usefulness, even when different methods of dosage are used, are anyway scarce.
OBJECTIVE: To compare the diagnostic performance in the NSC dosage of the chemiluminescence method (CLIA) and of mass spectrometry (LC-MS/MS).
METHODS: Saliva samples were taken at 11:00 pm in 36 healthy volunteers and in 10 patients with Cushings syndrome at the diagnosis. Each subject provided 2 saliva samples which were used for the NCS dosage by CLIA and with LC-MS/MS.
RESULTS: The controls had NSC values in LC-MS/MS (0.89l±0.37 ng/ml; range 0.101.89) significantly lower than the Cushing ones (3.18l±1.86 ng/ml; range 0.986.19); the same using CLIA: the NCS in the controls (0.40±0.22 mcg/dl; range 0.181.05) was significantly lower than the Cushing ones (1.43±0.66 mcg/dl; range 0.022.29). The diagnostic performance in LC-MS/MS [AUC 0.94 (0.861.02] was a bit higher than that of the CLIA [AUC 0.89 (0.711.07)]. The cutoff able to guarantee the highest sensitivity and specificity was calculated through the ROC curve, and it was to 1.2 ng/ml in LC-MS and 0.58 mcg/dl in CLIA. In LC-MS/MS a 90% sensitivity and a 88% specificity were obtained; for CLIA, a 90% sensitivity and a 84.8% specificity; if the cut off provided from the lab was used (0.2 mcg/dl), an unacceptably low performance was obtained. The values in CLIA related significantly to those in LCMS/MS (r 0.9).
CONCLUSIONS: This is the first study which compares a CLIA method with a method such as LC-MS/MS. Our data demonstrate that the cutoffs are highly influenced by the method being used. The analyzed methods can have a similar performance, provided the cutoffs are redefined in the single labs.
Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.
05 - 09 May 2012
European Society of Endocrinology