Investigation for Paediatric Cushing's Syndrome Using Twenty-Four-Hour Urinary Free Cortisol Determination.

OBJECTIVE Paediatric Cushing's syndrome (CS) remains a challenge to diagnose and exclude. We assessed the accuracy of 24-hour urinary free cortisol (UFC) determination in children referred for suspected CS. DESIGN We conducted a retrospective study of paediatric patients referred to our centre with suspected CS between 1982 and 2014. PATIENTS Of 66 subjects (mean age 12.9 years; range 4.4-16.9), there were 47 cases of CS (29 males), which included Cushing's disease (CD; 39 patients, 25 males), primary pigmented nodular adrenocortical disease (8 patients, 4 males) and 19 'controls' (6 males) in whom the diagnosis of CS was excluded. MEASUREMENTS The subjects had between one and five 24-hour UFC collections analysed by radioimmunoassay, chemiluminescent immunoassay or liquid chromatography-mass spectrometry. The data were normalised, corrected for body surface area (m2) and assessed using receiver operating characteristic analysis and an independent two-tailed t test. RESULTS The diagnostic accuracy of 24-hour UFC for CS was excellent (area under the curve 0.98, 95% CI 0.946-1.00, sensitivity 89%, specificity 100%). CONCLUSIONS Twenty-four-hour UFC is a reliable and practical investigation with high diagnostic accuracy for paediatric CS. However, further investigations may be required if the UFC is normal but there is a high diagnostic suspicion of CS.