Endocrine Abstracts

Background: Endogenous Cushing’s syndrome (CS) in children remains a challenge to diagnose and exclude. 24-h urinary free cortisol (UFC) measurements are a convenient, non-invasive test for paediatric patients.

Objective: To assess the screening accuracy of 24-h UFC measurements in paediatric patients referred to our centre for evaluation of possible CS.

Methods: A retrospective review of children referred to our centre between 1982 and 2014 was undertaken. The series included 62 children: 34 cases of Cushing’s disease (CD), eight bilateral micronodular adrenocortical disease, two ectopic ACTH secondary to bronchial carcinoid tumours and 18 controls (CS was excluded).

Results: All but three CS patients had elevated 24-h UFC measurements: mean 1380 nmol/24 h by immunoassay (normal range 40–340 nmol/l) and 767 nmol/24 h by LCMS assay (normal range <124 nmol/l). Mean values were 904 nmol/24 h for CS, 1132 nmol/24 h for adrenocortical disease, and 2244 nmol/24 h for ectopic tumours. Mean 24 h UFC values were significantly higher in males compared to females with CD (1088 nmol/24 h vs 635 nmol/24 h, respectively; P=0.004). In contrast, there was no difference in UFC levels between males and females in the control group (104 nmol/24 h and 119 nmol/24 h, respectively). The sensitivity and specificity for 24 h UFC measurements in the diagnosis of paediatric CS were both 93%. The false positive rate was 7% (2/27), and so was the false negative rate (3/44). Overall, the diagnostic accuracy (AUC) for 24 h UFC measurements was excellent (0.97, 95% CI 0.901–0.996).

Conclusions: 24-h UFC measurements have high diagnostic accuracy for CS in children and may be more sensitive as a diagnostic test for CS in paediatric compared to adult patients. Additionally, this test is widely available and can be performed at home. Interestingly, UFC concentrations were significantly higher in male compared to female CD patients.