Endocrine Abstracts

Endogenous Cushing’s syndrome poses considerable diagnostic challenges. It is recommended to use two screening tests to confirm hypercortisolaemia. While late-night salivary cortisol assessment (LNSC) is reported to have good specificity and sensitivity and deemed to be cost-effective, it is the least widely biochemical tool used both nationally and in Europe. We aim to compare the specificity and sensitivity of LNSC against and in combination with other diagnostic tests, within a heterogenous cohort who were referred with symptoms of hypercortisolaemia to a single tertiary centre. Sixty-nine patients screened for hypercortisolaemia were retrospectively reviewed. All patients had been asked to perform a midnight salivary cortisol test at home. 66 valid samples were returned. Further tests for hypercortisolaemia had also been performed, chosen based on patient and clinician preference: overnight dexamethasone suppression test (ODST) (n=33), low-dose 48-hour dexamethasone suppression test (LDDST) (n=20) and urinary free cortisol (UFC) (n=17). The patients were then categorised as follows; true hypercortisolaemia (n=22) defined by response to treatment and/or diagnostic histology, or no hypercortisolaemia (n=25). The specificity and sensitivity for these tests were calculated. Overall, 47 patients had both a LNSC and a second biochemical test for hypercortisolaemia. Median BMI across the cohort measured 35 (IQR 25–40) kg/m². Specificity and sensitivity were as follows: LNSC specificity 92%, sensitivity 86%. ODST specificity 71%, sensitivity 100%. LDDST specificity 73%, sensitivity 100%. UFC specificity 67%, sensitivity 55%. A combination of LNSC and LDDST or ODST suggests specificity of 98% and sensitivity of 86%. A combination of LDDST and ODST suggests specificity of 92% and sensitivity of 100%. These preliminary data have demonstrated LNSC to have superior specificity for determining hypercortisolaemia. Furthermore, our data suggests that the combination of LNSC/ODST is preferable to LDDST/ODST, thus reducing length of hospital admission required for diagnosis.